<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:0dc3fcc8-666e-44c2-a271-c2ec7fa3b34a,g:13591745-c79c-4f4b-b0b3-2cbde32f1614-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.bandwidth.com/role/Cover" xlink:type="simple" xlink:href="band-20241231.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_0875529d-3fce-405d-a57a-5a3c2243398f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntitiesTable_0875529d-3fce-405d-a57a-5a3c2243398f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_db987e90-16b7-4c24-97cb-6cb955d9768b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_0875529d-3fce-405d-a57a-5a3c2243398f" xlink:to="loc_us-gaap_StatementClassOfStockAxis_db987e90-16b7-4c24-97cb-6cb955d9768b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_db987e90-16b7-4c24-97cb-6cb955d9768b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_db987e90-16b7-4c24-97cb-6cb955d9768b" xlink:to="loc_us-gaap_ClassOfStockDomain_db987e90-16b7-4c24-97cb-6cb955d9768b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_910c7b8c-930c-450a-a6cf-4f4df1ffb4d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_db987e90-16b7-4c24-97cb-6cb955d9768b" xlink:to="loc_us-gaap_ClassOfStockDomain_910c7b8c-930c-450a-a6cf-4f4df1ffb4d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_a8b97ea2-3247-4131-88e4-394f6b0ba375" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_910c7b8c-930c-450a-a6cf-4f4df1ffb4d4" xlink:to="loc_us-gaap_CommonClassAMember_a8b97ea2-3247-4131-88e4-394f6b0ba375" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_88eda54b-093a-4e27-9003-edc3e0f5b5cc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_910c7b8c-930c-450a-a6cf-4f4df1ffb4d4" xlink:to="loc_us-gaap_CommonClassBMember_88eda54b-093a-4e27-9003-edc3e0f5b5cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_4b85a36f-bdb9-437d-a91a-3691b725b648" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentType_4b85a36f-bdb9-437d-a91a-3691b725b648" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentAnnualReport_0a816b9d-f43b-4449-99ab-77c5d8108a8a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentAnnualReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentAnnualReport_0a816b9d-f43b-4449-99ab-77c5d8108a8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_f287d016-a95b-44fa-b239-41325d41698c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentPeriodEndDate_f287d016-a95b-44fa-b239-41325d41698c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_bc2e9c53-ac25-4dd1-8579-584bd6f17769" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_CurrentFiscalYearEndDate_bc2e9c53-ac25-4dd1-8579-584bd6f17769" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_0884e3be-5ff1-49a8-9f7a-62520c2e8a7a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentTransitionReport_0884e3be-5ff1-49a8-9f7a-62520c2e8a7a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_4630e334-3fca-4fe5-ad46-bd6644150feb" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityFileNumber_4630e334-3fca-4fe5-ad46-bd6644150feb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_ca34630d-22e0-4db9-bb2c-a74a066d8f0d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityRegistrantName_ca34630d-22e0-4db9-bb2c-a74a066d8f0d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_bf30f6e0-292d-4139-896f-bceeb20c8616" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityIncorporationStateCountryCode_bf30f6e0-292d-4139-896f-bceeb20c8616" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_913a08c3-64d9-4f04-a0d8-bea6c6d5fc20" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityTaxIdentificationNumber_913a08c3-64d9-4f04-a0d8-bea6c6d5fc20" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_ac2069d2-8e60-45c4-a262-5bbb1995fc31" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityAddressAddressLine1_ac2069d2-8e60-45c4-a262-5bbb1995fc31" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_e76b325c-4a62-4ccb-b9c5-339d4bedfab7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityAddressCityOrTown_e76b325c-4a62-4ccb-b9c5-339d4bedfab7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_b5f6d3a1-64ff-4ffa-81da-cb89ccd42e15" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityAddressStateOrProvince_b5f6d3a1-64ff-4ffa-81da-cb89ccd42e15" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_b0db08d0-c779-49b6-b427-68ea55a29aa7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityAddressPostalZipCode_b0db08d0-c779-49b6-b427-68ea55a29aa7" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_26671e4d-04ef-4119-8bbd-1aa3012e549e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_CityAreaCode_26671e4d-04ef-4119-8bbd-1aa3012e549e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_8ef6c856-d562-4b4a-a184-34c75fe06d93" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_LocalPhoneNumber_8ef6c856-d562-4b4a-a184-34c75fe06d93" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_3f968f09-d384-41ba-a852-6b4e5af7b59c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_Security12bTitle_3f968f09-d384-41ba-a852-6b4e5af7b59c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_2085f8ed-d6fd-4f73-81c1-5bee4d0fddd2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_TradingSymbol_2085f8ed-d6fd-4f73-81c1-5bee4d0fddd2" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_ee194940-e7ee-462a-a036-1fb51e94baf6" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_SecurityExchangeName_ee194940-e7ee-462a-a036-1fb51e94baf6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityWellKnownSeasonedIssuer_7829a83b-8b3f-4ee6-a42f-64c23b525277" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityWellKnownSeasonedIssuer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityWellKnownSeasonedIssuer_7829a83b-8b3f-4ee6-a42f-64c23b525277" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityVoluntaryFilers_a42c96b7-f208-428a-8ec4-c56b8834b99c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityVoluntaryFilers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityVoluntaryFilers_a42c96b7-f208-428a-8ec4-c56b8834b99c" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_00bcbbc4-fc32-40e2-9abe-a4d485a36946" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityCurrentReportingStatus_00bcbbc4-fc32-40e2-9abe-a4d485a36946" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_5889e6e0-5c8a-4110-abfb-270fffa6564c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityInteractiveDataCurrent_5889e6e0-5c8a-4110-abfb-270fffa6564c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_5c1b577e-079a-463b-a00a-f24a95587527" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityFilerCategory_5c1b577e-079a-463b-a00a-f24a95587527" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_22119841-93ff-4e3b-bd4b-e13e96f8ef18" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntitySmallBusiness_22119841-93ff-4e3b-bd4b-e13e96f8ef18" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_fde8d445-1b53-4eaf-9001-839be5ff12c8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityEmergingGrowthCompany_fde8d445-1b53-4eaf-9001-839be5ff12c8" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag_bd48a81d-24e4-49a4-a92a-a8ab50155767" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_IcfrAuditorAttestationFlag_bd48a81d-24e4-49a4-a92a-a8ab50155767" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFinStmtErrorCorrectionFlag_8df23350-e231-4cf6-91a1-7dd51ee61623" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFinStmtErrorCorrectionFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentFinStmtErrorCorrectionFlag_8df23350-e231-4cf6-91a1-7dd51ee61623" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_1a46ef46-c1b4-40ec-9a84-4ecdcbf6833f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityShellCompany_1a46ef46-c1b4-40ec-9a84-4ecdcbf6833f" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityPublicFloat_66659758-7d22-4a7f-be85-dcee51712210" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityPublicFloat"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityPublicFloat_66659758-7d22-4a7f-be85-dcee51712210" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_179946e1-2525-4415-95de-16667470d3ce" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_179946e1-2525-4415-95de-16667470d3ce" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentsIncorporatedByReferenceTextBlock_845441ca-be4d-4e14-95de-543a61ef4774" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentsIncorporatedByReferenceTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentsIncorporatedByReferenceTextBlock_845441ca-be4d-4e14-95de-543a61ef4774" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_a3699e3a-aa80-4df9-8a61-a6986d5fe1e4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_EntityCentralIndexKey_a3699e3a-aa80-4df9-8a61-a6986d5fe1e4" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_f1d5ea45-f62f-477b-9be4-ad8910a19880" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentFiscalYearFocus_f1d5ea45-f62f-477b-9be4-ad8910a19880" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_9dd3701f-671e-4096-bbdf-b6c4729abad0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_DocumentFiscalPeriodFocus_9dd3701f-671e-4096-bbdf-b6c4729abad0" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_734b6ecf-76ac-4ea1-a44f-fd9381a0d2b0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_2210aa69-f928-460c-ac10-484d9f450039" xlink:to="loc_dei_AmendmentFlag_734b6ecf-76ac-4ea1-a44f-fd9381a0d2b0" xlink:type="arc" order="34"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/ConsolidatedBalanceSheets" xlink:type="simple" xlink:href="band-20241231.xsd#ConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_0dad9906-516d-43f7-8a06-6ca2faf381e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_c52dfa0c-1669-4765-91af-bbd24f39303d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0dad9906-516d-43f7-8a06-6ca2faf381e0" xlink:to="loc_us-gaap_StatementTable_c52dfa0c-1669-4765-91af-bbd24f39303d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_649817c4-145d-4fb9-a89b-e4d350bf8960" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_c52dfa0c-1669-4765-91af-bbd24f39303d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_649817c4-145d-4fb9-a89b-e4d350bf8960" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_649817c4-145d-4fb9-a89b-e4d350bf8960_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_649817c4-145d-4fb9-a89b-e4d350bf8960" xlink:to="loc_us-gaap_ClassOfStockDomain_649817c4-145d-4fb9-a89b-e4d350bf8960_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5fdf3697-e79b-4391-ab94-5dacd9485936" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_649817c4-145d-4fb9-a89b-e4d350bf8960" xlink:to="loc_us-gaap_ClassOfStockDomain_5fdf3697-e79b-4391-ab94-5dacd9485936" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_c1c5cca2-e0c2-4abb-bfea-11f96e7ba420" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5fdf3697-e79b-4391-ab94-5dacd9485936" xlink:to="loc_us-gaap_CommonClassAMember_c1c5cca2-e0c2-4abb-bfea-11f96e7ba420" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_423e671b-413f-4f5b-9830-f5b97d7af739" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5fdf3697-e79b-4391-ab94-5dacd9485936" xlink:to="loc_us-gaap_CommonClassBMember_423e671b-413f-4f5b-9830-f5b97d7af739" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0dad9906-516d-43f7-8a06-6ca2faf381e0" xlink:to="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_a32dbeef-2b76-48ba-b7e0-c7b6f626b53e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_a32dbeef-2b76-48ba-b7e0-c7b6f626b53e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesCurrent_5ea3280c-ad7b-4445-9b3a-e1a2f3d4aa47" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MarketableSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:to="loc_us-gaap_MarketableSecuritiesCurrent_5ea3280c-ad7b-4445-9b3a-e1a2f3d4aa47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_299ff9fe-0f33-4165-8846-492480288a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_299ff9fe-0f33-4165-8846-492480288a8c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCostsCurrent_70dc8378-bd2f-4789-810e-fd6c48d8811d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredCostsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:to="loc_us-gaap_DeferredCostsCurrent_70dc8378-bd2f-4789-810e-fd6c48d8811d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_f44ac4a9-c85a-404a-998e-28d5b70a7d71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_f44ac4a9-c85a-404a-998e-28d5b70a7d71" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_d2de1f78-37f4-43dc-9d39-ba72c9f64f28" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_016abf92-fd6e-4417-b097-bf134d023b90" xlink:to="loc_us-gaap_AssetsCurrent_d2de1f78-37f4-43dc-9d39-ba72c9f64f28" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_a0889ad7-45b1-4105-bbb7-e0d5a2f4628f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_a0889ad7-45b1-4105-bbb7-e0d5a2f4628f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_65566507-45b3-469e-8a6f-bc897f3910cb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_65566507-45b3-469e-8a6f-bc897f3910cb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_bf57bc75-3715-4d39-8d54-1b48ebeceeb5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_bf57bc75-3715-4d39-8d54-1b48ebeceeb5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCosts_b08969d3-2c6d-4b13-814c-65b13f55c0c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_DeferredCosts_b08969d3-2c6d-4b13-814c-65b13f55c0c6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_b3355c7b-4912-4a9f-9516-56a73e7842ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_b3355c7b-4912-4a9f-9516-56a73e7842ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_f12df11d-04b9-4bb3-86b8-d95898270edd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_Goodwill_f12df11d-04b9-4bb3-86b8-d95898270edd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_fb63252e-a4d5-42fa-aada-ae447a244951" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_57bc8c8d-7634-43d4-a78f-fdabb7157a55" xlink:to="loc_us-gaap_Assets_fb63252e-a4d5-42fa-aada-ae447a244951" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0dad9906-516d-43f7-8a06-6ca2faf381e0" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_7987e6c1-e63b-4caf-9c2a-7804d3843736" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:to="loc_us-gaap_AccountsPayableCurrent_7987e6c1-e63b-4caf-9c2a-7804d3843736" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_5a4106cc-2b7f-4b3b-bea3-e3cbccfa680c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_5a4106cc-2b7f-4b3b-bea3-e3cbccfa680c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_d8e3ac33-1537-48b4-ac3c-75362039415a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_d8e3ac33-1537-48b4-ac3c-75362039415a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerRefundLiability_a467ad14-432e-4d5e-9cff-305184c51ab5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerRefundLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:to="loc_us-gaap_ContractWithCustomerRefundLiability_a467ad14-432e-4d5e-9cff-305184c51ab5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_f2c51cec-17be-4c45-8315-12a3b7245309" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_f2c51cec-17be-4c45-8315-12a3b7245309" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_a25f1edb-fddf-44fe-b490-9f8248726fae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_fbead8d9-2c98-42f3-8a12-b571dc52486b" xlink:to="loc_us-gaap_LiabilitiesCurrent_a25f1edb-fddf-44fe-b490-9f8248726fae" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_57d60af5-a606-4e43-8c16-ea8829440469" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_57d60af5-a606-4e43-8c16-ea8829440469" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_26cdd880-deeb-4adb-bfe7-6f4760e315ea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_26cdd880-deeb-4adb-bfe7-6f4760e315ea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_2ac9f75e-8590-41d1-ad6a-b2ff1ea34e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_2ac9f75e-8590-41d1-ad6a-b2ff1ea34e3b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_3d4a218a-8a65-4678-a5a9-515e5096e16d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_3d4a218a-8a65-4678-a5a9-515e5096e16d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_7ef07981-83e7-4fc5-8a81-16036e0865f8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_7ef07981-83e7-4fc5-8a81-16036e0865f8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_f2a250b4-705e-45d2-905a-0a26331058e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_Liabilities_f2a250b4-705e-45d2-905a-0a26331058e1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_7e1c9825-ea2f-4623-9b78-db3c0460e615" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_CommitmentsAndContingencies_7e1c9825-ea2f-4623-9b78-db3c0460e615" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_a2ef4772-dd54-4c5a-aab7-40c3b87055c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:to="loc_us-gaap_PreferredStockValue_a2ef4772-dd54-4c5a-aab7-40c3b87055c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_0dea45b7-04bf-48fe-8a1d-d43fe9202d43" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:to="loc_us-gaap_CommonStockValue_0dea45b7-04bf-48fe-8a1d-d43fe9202d43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_dec72559-be8e-4d75-948d-8a3c0744f6d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:to="loc_us-gaap_AdditionalPaidInCapital_dec72559-be8e-4d75-948d-8a3c0744f6d3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_4c87c434-5ece-40c7-a31c-7d95fa2939d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_4c87c434-5ece-40c7-a31c-7d95fa2939d8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_4ab1662f-21b9-4787-b6c2-5ec64858cdaf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_4ab1662f-21b9-4787-b6c2-5ec64858cdaf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b8bbde41-f9d1-41e5-a205-c9c10705028b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_acadc13b-d4a4-4926-a21c-6aad95801b0f" xlink:to="loc_us-gaap_StockholdersEquity_b8bbde41-f9d1-41e5-a205-c9c10705028b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_46595f40-1624-43db-8b16-4fc8b591066f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_b88f8408-9485-4f81-b1e7-1e4714359be4" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_46595f40-1624-43db-8b16-4fc8b591066f" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="band-20241231.xsd#ConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_c2893010-27e2-421f-9b3d-f22f35b29a9c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_StatementTable_c2893010-27e2-421f-9b3d-f22f35b29a9c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9890845a-4694-4bba-add3-5b6efc53a9bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_c2893010-27e2-421f-9b3d-f22f35b29a9c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9890845a-4694-4bba-add3-5b6efc53a9bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9890845a-4694-4bba-add3-5b6efc53a9bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9890845a-4694-4bba-add3-5b6efc53a9bd" xlink:to="loc_us-gaap_ClassOfStockDomain_9890845a-4694-4bba-add3-5b6efc53a9bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e7e7bcef-7597-4750-ae71-c94854632988" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9890845a-4694-4bba-add3-5b6efc53a9bd" xlink:to="loc_us-gaap_ClassOfStockDomain_e7e7bcef-7597-4750-ae71-c94854632988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_348f0fb8-21a1-44ba-8b85-eb50850af8f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e7e7bcef-7597-4750-ae71-c94854632988" xlink:to="loc_us-gaap_CommonClassAMember_348f0fb8-21a1-44ba-8b85-eb50850af8f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_1c93db02-305f-4753-abc2-7a9dce314619" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_e7e7bcef-7597-4750-ae71-c94854632988" xlink:to="loc_us-gaap_CommonClassBMember_1c93db02-305f-4753-abc2-7a9dce314619" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_af624861-ebd1-45a2-b952-230863c55c99" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_af624861-ebd1-45a2-b952-230863c55c99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_5bd2ca2b-4b1e-4123-ac81-7414423c13bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_5bd2ca2b-4b1e-4123-ac81-7414423c13bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_97529711-f737-4212-b2a7-e4d7128810d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_PreferredStockSharesIssued_97529711-f737-4212-b2a7-e4d7128810d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_af2c988b-eac9-48cf-9a43-87785b92bcfa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_af2c988b-eac9-48cf-9a43-87785b92bcfa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_1733e203-9c82-411b-9ff0-a41943167af2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_1733e203-9c82-411b-9ff0-a41943167af2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_a1bec0b8-0511-4094-b7aa-80a3c970700a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_a1bec0b8-0511-4094-b7aa-80a3c970700a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_02d90b52-e158-42c4-ad02-99f3d66d8d02" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_CommonStockSharesIssued_02d90b52-e158-42c4-ad02-99f3d66d8d02" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_06d9a1a2-95a3-454d-9708-b0b5e0382752" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_dfc9fff2-f65d-4028-b1cb-239b56a9a1b4" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_06d9a1a2-95a3-454d-9708-b0b5e0382752" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/ConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="simple" xlink:href="band-20241231.xsd#ConsolidatedStatementsofChangesinStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/ConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c126e638-0bd8-42f4-96cd-fba459423012" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_accada0c-daec-485e-881b-53922eec3563" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c126e638-0bd8-42f4-96cd-fba459423012" xlink:to="loc_us-gaap_StatementTable_accada0c-daec-485e-881b-53922eec3563" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_c512c1e8-401a-4bc4-aedc-60625e78d68f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_accada0c-daec-485e-881b-53922eec3563" xlink:to="loc_us-gaap_StatementClassOfStockAxis_c512c1e8-401a-4bc4-aedc-60625e78d68f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c512c1e8-401a-4bc4-aedc-60625e78d68f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c512c1e8-401a-4bc4-aedc-60625e78d68f" xlink:to="loc_us-gaap_ClassOfStockDomain_c512c1e8-401a-4bc4-aedc-60625e78d68f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d09d4f3c-14e2-445c-8a47-24aa4e4574d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c512c1e8-401a-4bc4-aedc-60625e78d68f" xlink:to="loc_us-gaap_ClassOfStockDomain_d09d4f3c-14e2-445c-8a47-24aa4e4574d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_978ed0d9-12df-4f4d-a0f9-669ce5333fc0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d09d4f3c-14e2-445c-8a47-24aa4e4574d6" xlink:to="loc_us-gaap_CommonClassAMember_978ed0d9-12df-4f4d-a0f9-669ce5333fc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_51b80247-2418-4266-975f-031d19905c5e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d09d4f3c-14e2-445c-8a47-24aa4e4574d6" xlink:to="loc_us-gaap_CommonClassBMember_51b80247-2418-4266-975f-031d19905c5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_24b05fcf-117e-4b07-b6f1-1710e021c94a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_accada0c-daec-485e-881b-53922eec3563" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_24b05fcf-117e-4b07-b6f1-1710e021c94a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_24b05fcf-117e-4b07-b6f1-1710e021c94a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_24b05fcf-117e-4b07-b6f1-1710e021c94a" xlink:to="loc_us-gaap_EquityComponentDomain_24b05fcf-117e-4b07-b6f1-1710e021c94a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_bbe742a5-ddca-4b3f-8a96-09c7aa2a6126" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_24b05fcf-117e-4b07-b6f1-1710e021c94a" xlink:to="loc_us-gaap_EquityComponentDomain_bbe742a5-ddca-4b3f-8a96-09c7aa2a6126" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_9ec50995-9a75-4335-8e31-3343f4f31716" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_bbe742a5-ddca-4b3f-8a96-09c7aa2a6126" xlink:to="loc_us-gaap_CommonStockMember_9ec50995-9a75-4335-8e31-3343f4f31716" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_42e7576f-7e61-4fd6-a3d3-b7e221ac78b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_bbe742a5-ddca-4b3f-8a96-09c7aa2a6126" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_42e7576f-7e61-4fd6-a3d3-b7e221ac78b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_bcdb7a19-87d8-4911-829f-d532e259f82a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_bbe742a5-ddca-4b3f-8a96-09c7aa2a6126" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_bcdb7a19-87d8-4911-829f-d532e259f82a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_39155e5a-b234-49c7-8af5-d86eb81fd708" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_bbe742a5-ddca-4b3f-8a96-09c7aa2a6126" xlink:to="loc_us-gaap_RetainedEarningsMember_39155e5a-b234-49c7-8af5-d86eb81fd708" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_8e85e696-b9fd-488c-9a51-8e2eabad4cd5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_accada0c-daec-485e-881b-53922eec3563" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_8e85e696-b9fd-488c-9a51-8e2eabad4cd5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_8e85e696-b9fd-488c-9a51-8e2eabad4cd5_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_8e85e696-b9fd-488c-9a51-8e2eabad4cd5" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_8e85e696-b9fd-488c-9a51-8e2eabad4cd5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_37bf722d-7244-4db4-9f9e-da78591dcb35" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_8e85e696-b9fd-488c-9a51-8e2eabad4cd5" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_37bf722d-7244-4db4-9f9e-da78591dcb35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_8dea4acf-756c-4583-aeb9-2f3dabcdc4cf" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_37bf722d-7244-4db4-9f9e-da78591dcb35" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_8dea4acf-756c-4583-aeb9-2f3dabcdc4cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c126e638-0bd8-42f4-96cd-fba459423012" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_8860bf54-b6cd-4fea-bec0-1a1b6a0e60dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_8860bf54-b6cd-4fea-bec0-1a1b6a0e60dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_5be4cd19-0970-4b06-b4f0-1c05d219310b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockholdersEquity_5be4cd19-0970-4b06-b4f0-1c05d219310b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_3409bdc0-e9e4-4c88-b3e8-043454a432f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_3409bdc0-e9e4-4c88-b3e8-043454a432f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_426c772e-33ca-4b05-b19f-db196348b5ab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_426c772e-33ca-4b05-b19f-db196348b5ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_dff97984-35cf-4bb2-a941-701e16bca6c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_dff97984-35cf-4bb2-a941-701e16bca6c3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_08a3690e-c657-47ee-b91b-c19820cbbc7c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_08a3690e-c657-47ee-b91b-c19820cbbc7c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_2c319792-343b-45b6-99aa-04d0d60e8b13" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_2c319792-343b-45b6-99aa-04d0d60e8b13" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_1c974c80-2d0c-471c-b38d-57dd7239634a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_1c974c80-2d0c-471c-b38d-57dd7239634a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_272ac59f-a1ba-4e5e-95c4-8567ad670ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_272ac59f-a1ba-4e5e-95c4-8567ad670ee2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_f0b76b82-e73d-45ad-b7bb-948c02861366" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_f0b76b82-e73d-45ad-b7bb-948c02861366" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesUnrealizedGainLoss_f93f9808-2b89-4fcd-a993-4ec5ff8242cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MarketableSecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_MarketableSecuritiesUnrealizedGainLoss_f93f9808-2b89-4fcd-a993-4ec5ff8242cd" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_20453c8a-765c-4322-ad12-0048612b3dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_20453c8a-765c-4322-ad12-0048612b3dd5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_907129a9-0a76-490f-853c-cbeb0040ed58" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_907129a9-0a76-490f-853c-cbeb0040ed58" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f583281d-be08-41f0-a704-e94073dc5c36" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f583281d-be08-41f0-a704-e94073dc5c36" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_931cc003-f02f-43d2-9fd2-71dfa1a18da8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_7dc9c290-7e16-46ab-98c4-c7a30e54a184" xlink:to="loc_us-gaap_NetIncomeLoss_931cc003-f02f-43d2-9fd2-71dfa1a18da8" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_bb163e54-99fb-4cbd-b1db-1ae71ce4c47c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4e45136a-c5cc-4e6d-8afe-23f4f8bac3dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesScheduleofRevenueByCategoryDetails" xlink:type="simple" xlink:href="band-20241231.xsd#SummaryofSignificantAccountingPoliciesScheduleofRevenueByCategoryDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesScheduleofRevenueByCategoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d3576c42-b12f-45d0-a4fe-b08606d5d5b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_c008a20d-20e9-4789-8f1d-1a7462f8e4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d3576c42-b12f-45d0-a4fe-b08606d5d5b7" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_c008a20d-20e9-4789-8f1d-1a7462f8e4bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_5ffe66f1-6501-4817-8355-e679f0c09459" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_c008a20d-20e9-4789-8f1d-1a7462f8e4bf" xlink:to="loc_srt_ProductOrServiceAxis_5ffe66f1-6501-4817-8355-e679f0c09459" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5ffe66f1-6501-4817-8355-e679f0c09459_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_5ffe66f1-6501-4817-8355-e679f0c09459" xlink:to="loc_srt_ProductsAndServicesDomain_5ffe66f1-6501-4817-8355-e679f0c09459_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_9b348038-7334-4ceb-b743-102b6914a0eb" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_5ffe66f1-6501-4817-8355-e679f0c09459" xlink:to="loc_srt_ProductsAndServicesDomain_9b348038-7334-4ceb-b743-102b6914a0eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CloudCommunicationsMember_71a67fcb-2552-4e57-8573-d32417193dad" xlink:href="band-20241231.xsd#band_CloudCommunicationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_9b348038-7334-4ceb-b743-102b6914a0eb" xlink:to="loc_band_CloudCommunicationsMember_71a67fcb-2552-4e57-8573-d32417193dad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_MessagingSurchargesMember_add9a011-c356-4f8d-9133-4db392b827cb" xlink:href="band-20241231.xsd#band_MessagingSurchargesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_9b348038-7334-4ceb-b743-102b6914a0eb" xlink:to="loc_band_MessagingSurchargesMember_add9a011-c356-4f8d-9133-4db392b827cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9dfcea1b-7d4b-402f-9b0b-40ca9c00e2c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d3576c42-b12f-45d0-a4fe-b08606d5d5b7" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9dfcea1b-7d4b-402f-9b0b-40ca9c00e2c8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails" xlink:type="simple" xlink:href="band-20241231.xsd#SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:to="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:to="loc_srt_ProductsAndServicesDomain_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:to="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CPaaSUsageBasedFeesMember_cafbc5a8-6d48-4ba2-9740-3145672f94aa" xlink:href="band-20241231.xsd#band_CPaaSUsageBasedFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:to="loc_band_CPaaSUsageBasedFeesMember_cafbc5a8-6d48-4ba2-9740-3145672f94aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CPaaSServiceFeesMember_b9e96cb5-3a3e-4ba6-997c-b1bca974f03c" xlink:href="band-20241231.xsd#band_CPaaSServiceFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:to="loc_band_CPaaSServiceFeesMember_b9e96cb5-3a3e-4ba6-997c-b1bca974f03c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_f8e77396-05c0-47f3-a8bc-336a7260ce05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_f8e77396-05c0-47f3-a8bc-336a7260ce05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a1aa6867-cbb7-401e-9a3f-b4cb6b3a0968" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a1aa6867-cbb7-401e-9a3f-b4cb6b3a0968" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_44c6371e-bccf-4c1a-88a7-ae185721174e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_44c6371e-bccf-4c1a-88a7-ae185721174e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_a9b28a23-e974-4bfa-ac3d-6f1dca6a4c01" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_a9b28a23-e974-4bfa-ac3d-6f1dca6a4c01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5dd57dbb-1c40-4552-a7b6-a3ceb79e0242" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5dd57dbb-1c40-4552-a7b6-a3ceb79e0242" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails_1" xlink:type="simple" xlink:href="band-20241231.xsd#SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails_1"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_3f34cd05-7657-4a76-9340-344aca12412a" xlink:to="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:to="loc_srt_ProductsAndServicesDomain_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_6f679a5b-9aa7-4e7d-8ab1-6c62f96cb746" xlink:to="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CPaaSUsageBasedFeesMember_cafbc5a8-6d48-4ba2-9740-3145672f94aa" xlink:href="band-20241231.xsd#band_CPaaSUsageBasedFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:to="loc_band_CPaaSUsageBasedFeesMember_cafbc5a8-6d48-4ba2-9740-3145672f94aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CPaaSServiceFeesMember_b9e96cb5-3a3e-4ba6-997c-b1bca974f03c" xlink:href="band-20241231.xsd#band_CPaaSServiceFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_919bcbe4-fb82-4fca-b2f8-c9512ff3a007" xlink:to="loc_band_CPaaSServiceFeesMember_b9e96cb5-3a3e-4ba6-997c-b1bca974f03c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a1aa6867-cbb7-401e-9a3f-b4cb6b3a0968" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a1aa6867-cbb7-401e-9a3f-b4cb6b3a0968" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_44c6371e-bccf-4c1a-88a7-ae185721174e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_44c6371e-bccf-4c1a-88a7-ae185721174e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_a9b28a23-e974-4bfa-ac3d-6f1dca6a4c01" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_a9b28a23-e974-4bfa-ac3d-6f1dca6a4c01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5dd57dbb-1c40-4552-a7b6-a3ceb79e0242" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_3c9217ac-49a4-44ba-8de6-60f54b27d50a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5dd57dbb-1c40-4552-a7b6-a3ceb79e0242" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesDeferredCostsandInternalUseSoftwareDevelopmentCostsDetails" xlink:type="simple" xlink:href="band-20241231.xsd#SummaryofSignificantAccountingPoliciesDeferredCostsandInternalUseSoftwareDevelopmentCostsDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesDeferredCostsandInternalUseSoftwareDevelopmentCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_34e1845d-a682-479b-b904-4c86454b5909" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_7bfe24d8-55a8-48c8-8354-7719ca027438" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_34e1845d-a682-479b-b904-4c86454b5909" xlink:to="loc_us-gaap_CapitalizedContractCostTable_7bfe24d8-55a8-48c8-8354-7719ca027438" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3f8d00a5-eeae-4bcc-866a-354822f8b1d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_7bfe24d8-55a8-48c8-8354-7719ca027438" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3f8d00a5-eeae-4bcc-866a-354822f8b1d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3f8d00a5-eeae-4bcc-866a-354822f8b1d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3f8d00a5-eeae-4bcc-866a-354822f8b1d5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3f8d00a5-eeae-4bcc-866a-354822f8b1d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_cb7eb99d-0f43-46b1-a8e9-cd6ce37a563e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3f8d00a5-eeae-4bcc-866a-354822f8b1d5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_cb7eb99d-0f43-46b1-a8e9-cd6ce37a563e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_4f192ac1-ba23-453c-80b3-787d47ae252b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_cb7eb99d-0f43-46b1-a8e9-cd6ce37a563e" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_4f192ac1-ba23-453c-80b3-787d47ae252b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_774752b4-79e6-43f1-bad6-adf819e4b5de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizedContractCostAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_34e1845d-a682-479b-b904-4c86454b5909" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_774752b4-79e6-43f1-bad6-adf819e4b5de" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="band-20241231.xsd#SummaryofSignificantAccountingPoliciesScheduleofFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_e0d2df8f-913e-4b80-91a4-ce34bf83e1b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff6be0fe-c90e-4d6f-af8f-e8372fad3008" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_e0d2df8f-913e-4b80-91a4-ce34bf83e1b9" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff6be0fe-c90e-4d6f-af8f-e8372fad3008" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_52644de7-2d4f-4273-859b-b87f1f023f0c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff6be0fe-c90e-4d6f-af8f-e8372fad3008" xlink:to="loc_srt_RangeAxis_52644de7-2d4f-4273-859b-b87f1f023f0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_52644de7-2d4f-4273-859b-b87f1f023f0c_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_52644de7-2d4f-4273-859b-b87f1f023f0c" xlink:to="loc_srt_RangeMember_52644de7-2d4f-4273-859b-b87f1f023f0c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3707a306-fabc-4993-8b25-532c38fbac7e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_52644de7-2d4f-4273-859b-b87f1f023f0c" xlink:to="loc_srt_RangeMember_3707a306-fabc-4993-8b25-532c38fbac7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_1216e1b7-2510-457e-a7fb-a66124e00531" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3707a306-fabc-4993-8b25-532c38fbac7e" xlink:to="loc_srt_MinimumMember_1216e1b7-2510-457e-a7fb-a66124e00531" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_8c9f11b6-edba-4511-ad3b-c460cba346bf" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3707a306-fabc-4993-8b25-532c38fbac7e" xlink:to="loc_srt_MaximumMember_8c9f11b6-edba-4511-ad3b-c460cba346bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e0de2243-1dcd-4a84-bdab-e996f4222974" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_ff6be0fe-c90e-4d6f-af8f-e8372fad3008" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e0de2243-1dcd-4a84-bdab-e996f4222974" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e0de2243-1dcd-4a84-bdab-e996f4222974_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e0de2243-1dcd-4a84-bdab-e996f4222974" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e0de2243-1dcd-4a84-bdab-e996f4222974_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d65637c8-0972-4c40-87ca-7414821c4d39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e0de2243-1dcd-4a84-bdab-e996f4222974" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d65637c8-0972-4c40-87ca-7414821c4d39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_f376f49e-aa9b-447f-b833-e214f811abfb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d65637c8-0972-4c40-87ca-7414821c4d39" xlink:to="loc_us-gaap_CustomerRelationshipsMember_f376f49e-aa9b-447f-b833-e214f811abfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_d2efb77f-96e6-4309-aa00-0770a0b301b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d65637c8-0972-4c40-87ca-7414821c4d39" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_d2efb77f-96e6-4309-aa00-0770a0b301b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_2095c329-66de-4256-b7c1-e8251e75ceb4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d65637c8-0972-4c40-87ca-7414821c4d39" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_2095c329-66de-4256-b7c1-e8251e75ceb4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_b8265c63-5c42-4a8e-8d5a-70ec09a4b077" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_e0d2df8f-913e-4b80-91a4-ce34bf83e1b9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_b8265c63-5c42-4a8e-8d5a-70ec09a4b077" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesStockBasedCompensationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#SummaryofSignificantAccountingPoliciesStockBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SummaryofSignificantAccountingPoliciesStockBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2cecb235-3bdc-481b-9a2f-96bf849840d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a021fa0b-d4a5-4b81-a7aa-72a696d7b44a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2cecb235-3bdc-481b-9a2f-96bf849840d6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a021fa0b-d4a5-4b81-a7aa-72a696d7b44a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1085cdb6-d6d6-4fe2-b76a-570c6f6b0e52" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a021fa0b-d4a5-4b81-a7aa-72a696d7b44a" xlink:to="loc_srt_RangeAxis_1085cdb6-d6d6-4fe2-b76a-570c6f6b0e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1085cdb6-d6d6-4fe2-b76a-570c6f6b0e52_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1085cdb6-d6d6-4fe2-b76a-570c6f6b0e52" xlink:to="loc_srt_RangeMember_1085cdb6-d6d6-4fe2-b76a-570c6f6b0e52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2dedde66-bc38-434f-9137-2f4bb40fce8c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1085cdb6-d6d6-4fe2-b76a-570c6f6b0e52" xlink:to="loc_srt_RangeMember_2dedde66-bc38-434f-9137-2f4bb40fce8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_55ed9908-ed5b-4e9d-b11c-5d1abf414369" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2dedde66-bc38-434f-9137-2f4bb40fce8c" xlink:to="loc_srt_MinimumMember_55ed9908-ed5b-4e9d-b11c-5d1abf414369" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_8e8c62f1-7b16-457e-a8d3-b5eab70a2060" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2dedde66-bc38-434f-9137-2f4bb40fce8c" xlink:to="loc_srt_MaximumMember_8e8c62f1-7b16-457e-a8d3-b5eab70a2060" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_6e774329-0cdb-4d47-a4fc-5dcd6fac9947" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a021fa0b-d4a5-4b81-a7aa-72a696d7b44a" xlink:to="loc_us-gaap_AwardTypeAxis_6e774329-0cdb-4d47-a4fc-5dcd6fac9947" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e774329-0cdb-4d47-a4fc-5dcd6fac9947_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6e774329-0cdb-4d47-a4fc-5dcd6fac9947" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e774329-0cdb-4d47-a4fc-5dcd6fac9947_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d723b2d3-e055-4f19-b8ad-6b9fcd38add5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6e774329-0cdb-4d47-a4fc-5dcd6fac9947" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d723b2d3-e055-4f19-b8ad-6b9fcd38add5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_StockOptionsAndRestrictedStockUnitsEmployeesMember_cdea5861-ac26-4092-884d-a313e89de46a" xlink:href="band-20241231.xsd#band_StockOptionsAndRestrictedStockUnitsEmployeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d723b2d3-e055-4f19-b8ad-6b9fcd38add5" xlink:to="loc_band_StockOptionsAndRestrictedStockUnitsEmployeesMember_cdea5861-ac26-4092-884d-a313e89de46a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_RestrictedStockUnitsNonEmployeeMember_0d9f7c6b-0245-49ec-9622-94c3953e29bd" xlink:href="band-20241231.xsd#band_RestrictedStockUnitsNonEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d723b2d3-e055-4f19-b8ad-6b9fcd38add5" xlink:to="loc_band_RestrictedStockUnitsNonEmployeeMember_0d9f7c6b-0245-49ec-9622-94c3953e29bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_9986d418-cd5f-40a4-9375-318dd6187103" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2cecb235-3bdc-481b-9a2f-96bf849840d6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_9986d418-cd5f-40a4-9375-318dd6187103" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueDetails" xlink:type="simple" xlink:href="band-20241231.xsd#FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/FairValueMeasurementsScheduleofFinancialAssetsMeasuredatFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_db38fa66-0e7c-4cb9-8552-0d3b75b24ea8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_db38fa66-0e7c-4cb9-8552-0d3b75b24ea8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_6ffb9d8e-373b-4362-8c98-c80fcd6fcec3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_db38fa66-0e7c-4cb9-8552-0d3b75b24ea8" xlink:to="loc_us-gaap_FinancialInstrumentAxis_6ffb9d8e-373b-4362-8c98-c80fcd6fcec3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6ffb9d8e-373b-4362-8c98-c80fcd6fcec3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_6ffb9d8e-373b-4362-8c98-c80fcd6fcec3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6ffb9d8e-373b-4362-8c98-c80fcd6fcec3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b6f1884f-a2e0-46b7-bd0b-00b1030f2fec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_6ffb9d8e-373b-4362-8c98-c80fcd6fcec3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b6f1884f-a2e0-46b7-bd0b-00b1030f2fec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_29b3104a-b716-4792-b82d-825a1dcb0950" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b6f1884f-a2e0-46b7-bd0b-00b1030f2fec" xlink:to="loc_us-gaap_MoneyMarketFundsMember_29b3104a-b716-4792-b82d-825a1dcb0950" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_07396212-a2d1-4e4e-be88-fd4854f801f0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b6f1884f-a2e0-46b7-bd0b-00b1030f2fec" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_07396212-a2d1-4e4e-be88-fd4854f801f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BankTimeDepositsMember_a4365534-d7e9-4762-9a1b-4e515ed89a51" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BankTimeDepositsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b6f1884f-a2e0-46b7-bd0b-00b1030f2fec" xlink:to="loc_us-gaap_BankTimeDepositsMember_a4365534-d7e9-4762-9a1b-4e515ed89a51" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_5e83b10d-9ec5-4d95-8224-e25a0db3fe3e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_b6f1884f-a2e0-46b7-bd0b-00b1030f2fec" xlink:to="loc_us-gaap_CommercialPaperMember_5e83b10d-9ec5-4d95-8224-e25a0db3fe3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a08973e6-0d9e-454f-9ab5-aaf29c8af257" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_db38fa66-0e7c-4cb9-8552-0d3b75b24ea8" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a08973e6-0d9e-454f-9ab5-aaf29c8af257" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a08973e6-0d9e-454f-9ab5-aaf29c8af257_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a08973e6-0d9e-454f-9ab5-aaf29c8af257" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a08973e6-0d9e-454f-9ab5-aaf29c8af257_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8fa9839c-b5b1-4a17-bfe3-618d2fc09088" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a08973e6-0d9e-454f-9ab5-aaf29c8af257" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8fa9839c-b5b1-4a17-bfe3-618d2fc09088" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_8103cea5-59fd-444d-9e25-911072d0bc28" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8fa9839c-b5b1-4a17-bfe3-618d2fc09088" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_8103cea5-59fd-444d-9e25-911072d0bc28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_7fb57f33-3d96-4a2f-ab65-20809b9fc640" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8fa9839c-b5b1-4a17-bfe3-618d2fc09088" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_7fb57f33-3d96-4a2f-ab65-20809b9fc640" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_c6316fb1-3191-458c-afa7-94dbb0b696ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8fa9839c-b5b1-4a17-bfe3-618d2fc09088" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_c6316fb1-3191-458c-afa7-94dbb0b696ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6a3cadb6-be05-4f8a-852b-ffaedcabab1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_db38fa66-0e7c-4cb9-8552-0d3b75b24ea8" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6a3cadb6-be05-4f8a-852b-ffaedcabab1f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_6a3cadb6-be05-4f8a-852b-ffaedcabab1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6a3cadb6-be05-4f8a-852b-ffaedcabab1f" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_6a3cadb6-be05-4f8a-852b-ffaedcabab1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_a53eb334-a534-42c5-a319-075fd6eddf77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6a3cadb6-be05-4f8a-852b-ffaedcabab1f" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_a53eb334-a534-42c5-a319-075fd6eddf77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_cdd591c5-770c-4f5e-a07b-f2b9e16e321d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_a53eb334-a534-42c5-a319-075fd6eddf77" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_cdd591c5-770c-4f5e-a07b-f2b9e16e321d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_1498f00c-d92c-4f1c-916b-0979ac5fecb9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_1498f00c-d92c-4f1c-916b-0979ac5fecb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_8f726835-4240-40a6-9039-0fbc185cddae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_8f726835-4240-40a6-9039-0fbc185cddae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_12bfbaa1-9d71-489e-aa64-7023303e31be" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_12bfbaa1-9d71-489e-aa64-7023303e31be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_936404bd-5864-4abd-8e5f-4c8c30c3a43e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_936404bd-5864-4abd-8e5f-4c8c30c3a43e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_60c9d6f2-4625-4b94-969f-32f3a8915161" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_60c9d6f2-4625-4b94-969f-32f3a8915161" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_c7ab21cc-168e-4692-b77e-bcd6b3ec1abd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_c7ab21cc-168e-4692-b77e-bcd6b3ec1abd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_aac4cd63-0de2-417e-a114-565ad63320fd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_23da9bbe-3ee8-49b2-8efc-5c4bab8f14cd" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_aac4cd63-0de2-417e-a114-565ad63320fd" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/FairValueMeasurementsAdditionalInformationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#FairValueMeasurementsAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/FairValueMeasurementsAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_c408e6e3-3c1a-4779-86b9-45c57ba46846" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_DebtInstrumentTable_c408e6e3-3c1a-4779-86b9-45c57ba46846" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_e6a6d651-a147-4ea1-9868-c51127584eeb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_c408e6e3-3c1a-4779-86b9-45c57ba46846" xlink:to="loc_us-gaap_DebtInstrumentAxis_e6a6d651-a147-4ea1-9868-c51127584eeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_e6a6d651-a147-4ea1-9868-c51127584eeb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_e6a6d651-a147-4ea1-9868-c51127584eeb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_e6a6d651-a147-4ea1-9868-c51127584eeb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_59ed36e3-f152-4ab6-a968-3532f52e20a0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_e6a6d651-a147-4ea1-9868-c51127584eeb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_59ed36e3-f152-4ab6-a968-3532f52e20a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_7451eace-479a-4845-8c80-880bb8fcdda2" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_59ed36e3-f152-4ab6-a968-3532f52e20a0" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_7451eace-479a-4845-8c80-880bb8fcdda2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_7c5b22bb-0c0d-4ec9-b405-fbeacd340988" xlink:href="band-20241231.xsd#band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_59ed36e3-f152-4ab6-a968-3532f52e20a0" xlink:to="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_7c5b22bb-0c0d-4ec9-b405-fbeacd340988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_b7524d9b-81f7-4bf0-9b81-982df8babfc5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_c408e6e3-3c1a-4779-86b9-45c57ba46846" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_b7524d9b-81f7-4bf0-9b81-982df8babfc5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b7524d9b-81f7-4bf0-9b81-982df8babfc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b7524d9b-81f7-4bf0-9b81-982df8babfc5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b7524d9b-81f7-4bf0-9b81-982df8babfc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_5ba99603-7190-45e5-8594-62e138786b06" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b7524d9b-81f7-4bf0-9b81-982df8babfc5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_5ba99603-7190-45e5-8594-62e138786b06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_64ae1895-96ea-4e86-b7ed-1440edb6f63b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_5ba99603-7190-45e5-8594-62e138786b06" xlink:to="loc_us-gaap_ConvertibleDebtMember_64ae1895-96ea-4e86-b7ed-1440edb6f63b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_a2269581-e6bf-4380-9b5b-b7ea446c67e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_c408e6e3-3c1a-4779-86b9-45c57ba46846" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_a2269581-e6bf-4380-9b5b-b7ea446c67e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_a2269581-e6bf-4380-9b5b-b7ea446c67e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_a2269581-e6bf-4380-9b5b-b7ea446c67e1" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_a2269581-e6bf-4380-9b5b-b7ea446c67e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_89e7e6cf-307f-4a97-b9d4-aa45ff61b63b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_a2269581-e6bf-4380-9b5b-b7ea446c67e1" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_89e7e6cf-307f-4a97-b9d4-aa45ff61b63b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_644cdddc-9123-4bfa-a8ff-69dd45801a92" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_89e7e6cf-307f-4a97-b9d4-aa45ff61b63b" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_644cdddc-9123-4bfa-a8ff-69dd45801a92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_1e6022b2-011b-4855-91f7-91b7917f6999" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_1e6022b2-011b-4855-91f7-91b7917f6999" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_395bb5d4-d886-4f03-9afb-becfa71bbd17" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_395bb5d4-d886-4f03-9afb-becfa71bbd17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_60e7c3e9-0f1c-4065-b489-fa5faa103222" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_InvestmentIncomeInterest_60e7c3e9-0f1c-4065-b489-fa5faa103222" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_dee13dbf-7cbe-4af1-97b7-77845b23c8df" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLoss_dee13dbf-7cbe-4af1-97b7-77845b23c8df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList_e5dc1909-4efa-40dd-a45e-c073eec164a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_FinancingReceivableAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList_e5dc1909-4efa-40dd-a45e-c073eec164a6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_a88cb26e-dffe-4cc3-a735-37b99ced1700" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_LongTermDebtFairValue_a88cb26e-dffe-4cc3-a735-37b99ced1700" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_f797b4c0-3c19-44c7-b937-22344b641bad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b8b656e9-38c0-42fc-87e0-15f5d78c9f30" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_f797b4c0-3c19-44c7-b937-22344b641bad" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/LeasesAdditionalInformationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#LeasesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/LeasesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_00687b58-54df-436c-8003-3a5787c3c26d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_00687b58-54df-436c-8003-3a5787c3c26d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_4d4cf717-9fe7-49fe-b1a6-b1f685f7d618" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_00687b58-54df-436c-8003-3a5787c3c26d" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_4d4cf717-9fe7-49fe-b1a6-b1f685f7d618" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_4d4cf717-9fe7-49fe-b1a6-b1f685f7d618_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_4d4cf717-9fe7-49fe-b1a6-b1f685f7d618" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_4d4cf717-9fe7-49fe-b1a6-b1f685f7d618_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_93537d4a-9669-4ee5-b185-eafc616daab8" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_4d4cf717-9fe7-49fe-b1a6-b1f685f7d618" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_93537d4a-9669-4ee5-b185-eafc616daab8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CorporateHeadquartersMember_f47b5ffa-0928-4df6-85bb-89cfa2d9c324" xlink:href="band-20241231.xsd#band_CorporateHeadquartersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_93537d4a-9669-4ee5-b185-eafc616daab8" xlink:to="loc_band_CorporateHeadquartersMember_f47b5ffa-0928-4df6-85bb-89cfa2d9c324" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseRenewalTerm_284e4858-9e4a-4c91-be7d-7407c7c990e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LessorOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_LessorOperatingLeaseRenewalTerm_284e4858-9e4a-4c91-be7d-7407c7c990e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseCost_93dafccc-ada8-4544-b27c-4aff8006ed56" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_OperatingLeaseCost_93dafccc-ada8-4544-b27c-4aff8006ed56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermLeaseCost_f877671f-4e05-4e6e-b034-d80a4dd8a7e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_ShortTermLeaseCost_f877671f-4e05-4e6e-b034-d80a4dd8a7e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_OperatingLeaseRightOfUseAssetAccumulatedAmortization_8b95b26a-3879-41ed-9ade-f4880fde2943" xlink:href="band-20241231.xsd#band_OperatingLeaseRightOfUseAssetAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_band_OperatingLeaseRightOfUseAssetAccumulatedAmortization_8b95b26a-3879-41ed-9ade-f4880fde2943" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_bb0c9941-4521-4896-88bd-6b174008df71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_bb0c9941-4521-4896-88bd-6b174008df71" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_LesseeOperatingLeaseNumberOfOptionToExtend_79e89ec6-794d-4a0d-b478-226b0d7571ca" xlink:href="band-20241231.xsd#band_LesseeOperatingLeaseNumberOfOptionToExtend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_band_LesseeOperatingLeaseNumberOfOptionToExtend_79e89ec6-794d-4a0d-b478-226b0d7571ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_ddeff2d1-cdf8-443f-97a0-f9dabd942cd0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_ddeff2d1-cdf8-443f-97a0-f9dabd942cd0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_MarketRentalRate_050350d6-df05-421d-996b-4564f5491747" xlink:href="band-20241231.xsd#band_MarketRentalRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_band_MarketRentalRate_050350d6-df05-421d-996b-4564f5491747" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseDiscountRate_d8b2ee50-0338-498c-bc54-8eba9eed5b19" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_LesseeOperatingLeaseDiscountRate_d8b2ee50-0338-498c-bc54-8eba9eed5b19" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_073d8eb2-ae7c-4937-a100-421e17676417" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_073d8eb2-ae7c-4937-a100-421e17676417" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_c91a532b-e08e-403f-a392-d2df8afe2552" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_OperatingLeaseLiability_c91a532b-e08e-403f-a392-d2df8afe2552" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_LeaseIncentive_41aa3fba-99ca-435b-8851-30d5c4b6c034" xlink:href="band-20241231.xsd#band_LeaseIncentive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_band_LeaseIncentive_41aa3fba-99ca-435b-8851-30d5c4b6c034" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecurityDeposit_4718a615-7f09-43c5-9d7a-f5ea8114466e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecurityDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_SecurityDeposit_4718a615-7f09-43c5-9d7a-f5ea8114466e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EscrowDeposit_33939258-7535-4107-8a3e-e4db7b4c562e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_0edb4b35-6524-456e-b4e7-83d387d1e438" xlink:to="loc_us-gaap_EscrowDeposit_33939258-7535-4107-8a3e-e4db7b4c562e" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/PropertyPlantandEquipmentScheduleofPropertyPlantandEquipmentNetDetails" xlink:type="simple" xlink:href="band-20241231.xsd#PropertyPlantandEquipmentScheduleofPropertyPlantandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/PropertyPlantandEquipmentScheduleofPropertyPlantandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ccfadcb8-5610-41ff-ad92-059a33c22fb8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_58e4cbc0-3812-481f-93fa-030370f7f8ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ccfadcb8-5610-41ff-ad92-059a33c22fb8" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_58e4cbc0-3812-481f-93fa-030370f7f8ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f614a5eb-bb0e-4d62-a581-48e9c4658109" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_58e4cbc0-3812-481f-93fa-030370f7f8ac" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f614a5eb-bb0e-4d62-a581-48e9c4658109" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f614a5eb-bb0e-4d62-a581-48e9c4658109_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f614a5eb-bb0e-4d62-a581-48e9c4658109" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f614a5eb-bb0e-4d62-a581-48e9c4658109_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f614a5eb-bb0e-4d62-a581-48e9c4658109" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_bebe7213-b637-434a-8ff0-f7e565b8233c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_bebe7213-b637-434a-8ff0-f7e565b8233c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ComputerAndOfficeEquipmentMember_92919b69-13c4-40d3-bdc0-c7edfde8b145" xlink:href="band-20241231.xsd#band_ComputerAndOfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_band_ComputerAndOfficeEquipmentMember_92919b69-13c4-40d3-bdc0-c7edfde8b145" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_TelecommunicationsEquipmentMember_d2dfc893-7e97-4e56-823b-b2a6a31fda8d" xlink:href="band-20241231.xsd#band_TelecommunicationsEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_band_TelecommunicationsEquipmentMember_d2dfc893-7e97-4e56-823b-b2a6a31fda8d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_d3b2e7f6-28a8-4b20-82d8-8030d267cfeb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_d3b2e7f6-28a8-4b20-82d8-8030d267cfeb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_c673b2c5-9257-4c68-8708-169d2567111b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_c673b2c5-9257-4c68-8708-169d2567111b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_715b6d0a-979b-4929-8fd1-7fb39b3c7dc0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_715b6d0a-979b-4929-8fd1-7fb39b3c7dc0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AutomobilesMember_f9776cc2-d99c-433a-baeb-0f046442c0d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AutomobilesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_AutomobilesMember_f9776cc2-d99c-433a-baeb-0f046442c0d3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_2d0aef79-c9e0-42e6-a34d-5b7a9d80f46e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_LandMember_2d0aef79-c9e0-42e6-a34d-5b7a9d80f46e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandImprovementsMember_7cbbee1e-42e4-432d-b6f7-88d280ee0990" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LandImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_c2c6c83d-47a3-4eba-8ae8-99aa9941a7d8" xlink:to="loc_us-gaap_LandImprovementsMember_7cbbee1e-42e4-432d-b6f7-88d280ee0990" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_f8d4b025-36a6-44ea-b91a-e6f0e4ed7614" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_58e4cbc0-3812-481f-93fa-030370f7f8ac" xlink:to="loc_srt_RangeAxis_f8d4b025-36a6-44ea-b91a-e6f0e4ed7614" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f8d4b025-36a6-44ea-b91a-e6f0e4ed7614_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_f8d4b025-36a6-44ea-b91a-e6f0e4ed7614" xlink:to="loc_srt_RangeMember_f8d4b025-36a6-44ea-b91a-e6f0e4ed7614_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_cb2f33e7-326a-4217-a53a-1d3a1d7f3494" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_f8d4b025-36a6-44ea-b91a-e6f0e4ed7614" xlink:to="loc_srt_RangeMember_cb2f33e7-326a-4217-a53a-1d3a1d7f3494" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_e3f7eb47-602e-484f-8370-fbb5346ada1a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_cb2f33e7-326a-4217-a53a-1d3a1d7f3494" xlink:to="loc_srt_MinimumMember_e3f7eb47-602e-484f-8370-fbb5346ada1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_76c84e20-8fae-44c0-b172-8bc2a74ac7b3" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_cb2f33e7-326a-4217-a53a-1d3a1d7f3494" xlink:to="loc_srt_MaximumMember_76c84e20-8fae-44c0-b172-8bc2a74ac7b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_cd42cd09-283d-4e53-9fb6-92de8994722d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ccfadcb8-5610-41ff-ad92-059a33c22fb8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_cd42cd09-283d-4e53-9fb6-92de8994722d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_355b0290-9601-4fda-bfe4-92f9ec07e14c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ccfadcb8-5610-41ff-ad92-059a33c22fb8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_355b0290-9601-4fda-bfe4-92f9ec07e14c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_24a8dc73-6faa-456b-a447-04053036fbfa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ccfadcb8-5610-41ff-ad92-059a33c22fb8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_24a8dc73-6faa-456b-a447-04053036fbfa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_fcb4522f-970a-4043-95c6-025a1ce78e65" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_ccfadcb8-5610-41ff-ad92-059a33c22fb8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_fcb4522f-970a-4043-95c6-025a1ce78e65" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/PropertyPlantandEquipmentScheduleofDepreciationExpenseDetails" xlink:type="simple" xlink:href="band-20241231.xsd#PropertyPlantandEquipmentScheduleofDepreciationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/PropertyPlantandEquipmentScheduleofDepreciationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_e8051eb6-1d12-4b0f-a85e-87d115a47806" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_32051f0b-9901-4c8c-aac4-2d9b4a2bfa92" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_e8051eb6-1d12-4b0f-a85e-87d115a47806" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_32051f0b-9901-4c8c-aac4-2d9b4a2bfa92" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_aca6c30f-14ab-434e-b9a7-40236f2a65fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_32051f0b-9901-4c8c-aac4-2d9b4a2bfa92" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_aca6c30f-14ab-434e-b9a7-40236f2a65fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_aca6c30f-14ab-434e-b9a7-40236f2a65fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_aca6c30f-14ab-434e-b9a7-40236f2a65fc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_aca6c30f-14ab-434e-b9a7-40236f2a65fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a7ac9465-0041-46b9-9037-0920d95e4429" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_aca6c30f-14ab-434e-b9a7-40236f2a65fc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a7ac9465-0041-46b9-9037-0920d95e4429" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_420b622e-9ff2-42b8-9bb9-2e3900e6647b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7ac9465-0041-46b9-9037-0920d95e4429" xlink:to="loc_us-gaap_CostOfSalesMember_420b622e-9ff2-42b8-9bb9-2e3900e6647b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_eec63a16-7beb-4880-bde6-bcf755155ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7ac9465-0041-46b9-9037-0920d95e4429" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_eec63a16-7beb-4880-bde6-bcf755155ebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_7f338cbb-6dac-40be-a4ef-fbc6049579a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7ac9465-0041-46b9-9037-0920d95e4429" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_7f338cbb-6dac-40be-a4ef-fbc6049579a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_70e64495-f917-43ee-85df-f064418ccbb8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7ac9465-0041-46b9-9037-0920d95e4429" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_70e64495-f917-43ee-85df-f064418ccbb8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_624a778b-e3e3-464c-ba61-8f9d19c8b800" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_e8051eb6-1d12-4b0f-a85e-87d115a47806" xlink:to="loc_us-gaap_Depreciation_624a778b-e3e3-464c-ba61-8f9d19c8b800" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsNetDetails" xlink:type="simple" xlink:href="band-20241231.xsd#GoodwillandIntangibleAssetsScheduleofIntangibleAssetsNetDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_627096a1-8f92-4fb1-af21-647160045d3b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0427f51c-3447-4096-8c6c-d44735c2c35e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_627096a1-8f92-4fb1-af21-647160045d3b" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0427f51c-3447-4096-8c6c-d44735c2c35e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ed38025a-e09f-414e-8394-04a5ba15600e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0427f51c-3447-4096-8c6c-d44735c2c35e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ed38025a-e09f-414e-8394-04a5ba15600e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ed38025a-e09f-414e-8394-04a5ba15600e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ed38025a-e09f-414e-8394-04a5ba15600e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ed38025a-e09f-414e-8394-04a5ba15600e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_169d5383-99d6-4f58-8f13-ab7d3580f38a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ed38025a-e09f-414e-8394-04a5ba15600e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_169d5383-99d6-4f58-8f13-ab7d3580f38a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_5d86437c-1985-48ad-9b17-97384693703f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_169d5383-99d6-4f58-8f13-ab7d3580f38a" xlink:to="loc_us-gaap_CustomerRelationshipsMember_5d86437c-1985-48ad-9b17-97384693703f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_6b65b037-5435-43b0-83e0-5d73cff00544" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_169d5383-99d6-4f58-8f13-ab7d3580f38a" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_6b65b037-5435-43b0-83e0-5d73cff00544" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_1ed6c762-5e83-4319-8077-fa8928f06b68" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_169d5383-99d6-4f58-8f13-ab7d3580f38a" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_1ed6c762-5e83-4319-8077-fa8928f06b68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_876140c3-6d5f-437d-b273-ee4554fe93bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0427f51c-3447-4096-8c6c-d44735c2c35e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_876140c3-6d5f-437d-b273-ee4554fe93bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_876140c3-6d5f-437d-b273-ee4554fe93bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_876140c3-6d5f-437d-b273-ee4554fe93bd" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_876140c3-6d5f-437d-b273-ee4554fe93bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_7e39a8a7-0356-494b-9042-c1cc147d91d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_876140c3-6d5f-437d-b273-ee4554fe93bd" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_7e39a8a7-0356-494b-9042-c1cc147d91d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_47cb0eac-9a48-41fe-b14f-d51425aebead" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_7e39a8a7-0356-494b-9042-c1cc147d91d7" xlink:to="loc_us-gaap_LicensingAgreementsMember_47cb0eac-9a48-41fe-b14f-d51425aebead" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_627096a1-8f92-4fb1-af21-647160045d3b" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_c41156e7-aa16-47e4-ba78-996aa548f3aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_c41156e7-aa16-47e4-ba78-996aa548f3aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_e7bc2908-12ba-48a2-afb4-9e6eefa2c4d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_e7bc2908-12ba-48a2-afb4-9e6eefa2c4d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8c877548-4ccc-4b2c-8675-09fbd34962cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8c877548-4ccc-4b2c-8675-09fbd34962cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_b0eb0d49-6350-47bd-b351-8b0ffda16434" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_b0eb0d49-6350-47bd-b351-8b0ffda16434" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_f99a5771-bb87-4d8b-8a32-139cedef6b77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_f99a5771-bb87-4d8b-8a32-139cedef6b77" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_3450d1c1-f14d-4675-97e3-d66b6c514598" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_a39278d2-a1e5-41a2-9cb1-3f0519f3810f" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_3450d1c1-f14d-4675-97e3-d66b6c514598" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/GoodwillandIntangibleAssetsScheduleofAmortizationExpenseDetails" xlink:type="simple" xlink:href="band-20241231.xsd#GoodwillandIntangibleAssetsScheduleofAmortizationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/GoodwillandIntangibleAssetsScheduleofAmortizationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_0453bd11-6469-4887-9e9a-3f5b9d83e5bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_a1db16e1-ab99-492b-96ab-97adffa686a7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_0453bd11-6469-4887-9e9a-3f5b9d83e5bf" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_a1db16e1-ab99-492b-96ab-97adffa686a7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_11d661db-1a9f-4a8e-9d53-6da16c38ffea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_a1db16e1-ab99-492b-96ab-97adffa686a7" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_11d661db-1a9f-4a8e-9d53-6da16c38ffea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_11d661db-1a9f-4a8e-9d53-6da16c38ffea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_11d661db-1a9f-4a8e-9d53-6da16c38ffea" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_11d661db-1a9f-4a8e-9d53-6da16c38ffea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_32ed60c2-1690-491f-a4d5-c4ac36ee2840" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_11d661db-1a9f-4a8e-9d53-6da16c38ffea" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_32ed60c2-1690-491f-a4d5-c4ac36ee2840" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_78cd5e55-e300-49d2-8af8-151be2a7eea9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_32ed60c2-1690-491f-a4d5-c4ac36ee2840" xlink:to="loc_us-gaap_CostOfSalesMember_78cd5e55-e300-49d2-8af8-151be2a7eea9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_56dabf95-aaa6-42ee-a3e6-1ad2faaacf4c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_32ed60c2-1690-491f-a4d5-c4ac36ee2840" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_56dabf95-aaa6-42ee-a3e6-1ad2faaacf4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_0b6825c9-6d7f-4c47-8d3b-fc171c65fcf6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_0453bd11-6469-4887-9e9a-3f5b9d83e5bf" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_0b6825c9-6d7f-4c47-8d3b-fc171c65fcf6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/DebtRevolvingCreditFacilityDetails" xlink:type="simple" xlink:href="band-20241231.xsd#DebtRevolvingCreditFacilityDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/DebtRevolvingCreditFacilityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d1c3cff5-94d5-4f66-9a22-cd722ab92979" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_CreditFacilityAxis_d1c3cff5-94d5-4f66-9a22-cd722ab92979" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d1c3cff5-94d5-4f66-9a22-cd722ab92979_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d1c3cff5-94d5-4f66-9a22-cd722ab92979" xlink:to="loc_us-gaap_CreditFacilityDomain_d1c3cff5-94d5-4f66-9a22-cd722ab92979_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_a15fe604-bcfd-468e-aef5-d96f53267a96" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d1c3cff5-94d5-4f66-9a22-cd722ab92979" xlink:to="loc_us-gaap_CreditFacilityDomain_a15fe604-bcfd-468e-aef5-d96f53267a96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_f7a501ef-e7a4-4e0b-8cfc-3acdc3b6bbeb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a15fe604-bcfd-468e-aef5-d96f53267a96" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_f7a501ef-e7a4-4e0b-8cfc-3acdc3b6bbeb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_776ede29-94c5-456a-803a-26fd592774d2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a15fe604-bcfd-468e-aef5-d96f53267a96" xlink:to="loc_us-gaap_LetterOfCreditMember_776ede29-94c5-456a-803a-26fd592774d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_f6d43ea0-2211-4159-816f-3612a4cea829" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a15fe604-bcfd-468e-aef5-d96f53267a96" xlink:to="loc_us-gaap_BridgeLoanMember_f6d43ea0-2211-4159-816f-3612a4cea829" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_eb6c805e-3b9c-4d9e-818f-36e3e9b713fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_DebtInstrumentAxis_eb6c805e-3b9c-4d9e-818f-36e3e9b713fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_eb6c805e-3b9c-4d9e-818f-36e3e9b713fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_eb6c805e-3b9c-4d9e-818f-36e3e9b713fc" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_eb6c805e-3b9c-4d9e-818f-36e3e9b713fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_9fd7f397-557e-43dc-9284-e6aec82627b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_eb6c805e-3b9c-4d9e-818f-36e3e9b713fc" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_9fd7f397-557e-43dc-9284-e6aec82627b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_BankOfAmericaCreditAgreementMember_d696abc2-30a7-454d-818f-77fac6786550" xlink:href="band-20241231.xsd#band_BankOfAmericaCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_9fd7f397-557e-43dc-9284-e6aec82627b6" xlink:to="loc_band_BankOfAmericaCreditAgreementMember_d696abc2-30a7-454d-818f-77fac6786550" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_ebb7f90f-19e1-42d5-964e-8829f6dd986e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_ebb7f90f-19e1-42d5-964e-8829f6dd986e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ebb7f90f-19e1-42d5-964e-8829f6dd986e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ebb7f90f-19e1-42d5-964e-8829f6dd986e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ebb7f90f-19e1-42d5-964e-8829f6dd986e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e1ac0f36-d7f6-4693-8f64-4ebe3e59d9ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_ebb7f90f-19e1-42d5-964e-8829f6dd986e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e1ac0f36-d7f6-4693-8f64-4ebe3e59d9ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_6326fe0c-4bb8-4a6e-af2d-3ce73a11126e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e1ac0f36-d7f6-4693-8f64-4ebe3e59d9ac" xlink:to="loc_us-gaap_LineOfCreditMember_6326fe0c-4bb8-4a6e-af2d-3ce73a11126e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_50b6f965-b110-4a58-a757-d89284096801" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_VariableRateAxis_50b6f965-b110-4a58-a757-d89284096801" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_50b6f965-b110-4a58-a757-d89284096801_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_50b6f965-b110-4a58-a757-d89284096801" xlink:to="loc_us-gaap_VariableRateDomain_50b6f965-b110-4a58-a757-d89284096801_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_1c7cb48a-0121-424c-bac6-ec101c7f6251" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_50b6f965-b110-4a58-a757-d89284096801" xlink:to="loc_us-gaap_VariableRateDomain_1c7cb48a-0121-424c-bac6-ec101c7f6251" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_c703e3c3-5c88-4a03-82c6-a26b02fe6930" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_1c7cb48a-0121-424c-bac6-ec101c7f6251" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_c703e3c3-5c88-4a03-82c6-a26b02fe6930" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_30e4a3cb-1491-46a0-b228-c2323b810097" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_1c7cb48a-0121-424c-bac6-ec101c7f6251" xlink:to="loc_us-gaap_BaseRateMember_30e4a3cb-1491-46a0-b228-c2323b810097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_821b60a7-d094-4a61-a2f9-bffdc541334a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_srt_RangeAxis_821b60a7-d094-4a61-a2f9-bffdc541334a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_821b60a7-d094-4a61-a2f9-bffdc541334a_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_821b60a7-d094-4a61-a2f9-bffdc541334a" xlink:to="loc_srt_RangeMember_821b60a7-d094-4a61-a2f9-bffdc541334a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d8f5684b-8071-477d-b55b-f4882e5b7dd4" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_821b60a7-d094-4a61-a2f9-bffdc541334a" xlink:to="loc_srt_RangeMember_d8f5684b-8071-477d-b55b-f4882e5b7dd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_99a20a5b-5896-40f7-9e96-6b8ec3d4f1dc" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d8f5684b-8071-477d-b55b-f4882e5b7dd4" xlink:to="loc_srt_MinimumMember_99a20a5b-5896-40f7-9e96-6b8ec3d4f1dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e0b81496-6673-4e56-b7c9-ee9206c8e7c1" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_d8f5684b-8071-477d-b55b-f4882e5b7dd4" xlink:to="loc_srt_MaximumMember_e0b81496-6673-4e56-b7c9-ee9206c8e7c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_f67e6d52-33f9-4253-902f-1c8bf73b8563" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_f67e6d52-33f9-4253-902f-1c8bf73b8563" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f67e6d52-33f9-4253-902f-1c8bf73b8563_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_f67e6d52-33f9-4253-902f-1c8bf73b8563" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f67e6d52-33f9-4253-902f-1c8bf73b8563_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_be9cb134-1da3-4ddc-acee-323639ce16d2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_f67e6d52-33f9-4253-902f-1c8bf73b8563" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_be9cb134-1da3-4ddc-acee-323639ce16d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_3cab98f0-2f2d-4820-8beb-163ca08b69d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_be9cb134-1da3-4ddc-acee-323639ce16d2" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_3cab98f0-2f2d-4820-8beb-163ca08b69d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_c213a033-e66d-4437-b93f-323f96235a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_be9cb134-1da3-4ddc-acee-323639ce16d2" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_c213a033-e66d-4437-b93f-323f96235a4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_35f5788f-8958-4a10-86fd-46905651cdbc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_StatementClassOfStockAxis_35f5788f-8958-4a10-86fd-46905651cdbc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_35f5788f-8958-4a10-86fd-46905651cdbc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_35f5788f-8958-4a10-86fd-46905651cdbc" xlink:to="loc_us-gaap_ClassOfStockDomain_35f5788f-8958-4a10-86fd-46905651cdbc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8c48c78a-4fb7-471c-80eb-d315bad74ca4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_35f5788f-8958-4a10-86fd-46905651cdbc" xlink:to="loc_us-gaap_ClassOfStockDomain_8c48c78a-4fb7-471c-80eb-d315bad74ca4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_VotingCommonStockMember_6c53804f-e2a5-47b9-bd9b-615498bc9dd0" xlink:href="band-20241231.xsd#band_VotingCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8c48c78a-4fb7-471c-80eb-d315bad74ca4" xlink:to="loc_band_VotingCommonStockMember_6c53804f-e2a5-47b9-bd9b-615498bc9dd0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonvotingCommonStockMember_cbf09243-f2d1-4097-9a98-70c44135c87c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonvotingCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8c48c78a-4fb7-471c-80eb-d315bad74ca4" xlink:to="loc_us-gaap_NonvotingCommonStockMember_cbf09243-f2d1-4097-9a98-70c44135c87c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_29b13842-c7cb-4c45-a707-821d61da53da" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_119a10dd-9142-4492-b182-c805778a9353" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_29b13842-c7cb-4c45-a707-821d61da53da" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_29b13842-c7cb-4c45-a707-821d61da53da_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_29b13842-c7cb-4c45-a707-821d61da53da" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_29b13842-c7cb-4c45-a707-821d61da53da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_78f530aa-37fa-4607-b6f3-f4ebedaafdcb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_29b13842-c7cb-4c45-a707-821d61da53da" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_78f530aa-37fa-4607-b6f3-f4ebedaafdcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_0cb725c2-f874-473e-97be-4b7a000b807c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_78f530aa-37fa-4607-b6f3-f4ebedaafdcb" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_0cb725c2-f874-473e-97be-4b7a000b807c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_2d6f8af8-4f1b-458f-ac66-0dd73ec3d52c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNoncurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_78f530aa-37fa-4607-b6f3-f4ebedaafdcb" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_2d6f8af8-4f1b-458f-ac66-0dd73ec3d52c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_14fda696-3195-4f0e-95bd-017ced9d7647" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_14fda696-3195-4f0e-95bd-017ced9d7647" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_LineOfCreditFacilityAccordionFeatureIncreaseLimit_1576a90f-3e3e-4d42-91a8-2d8f73266625" xlink:href="band-20241231.xsd#band_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_LineOfCreditFacilityAccordionFeatureIncreaseLimit_1576a90f-3e3e-4d42-91a8-2d8f73266625" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_LineOfCreditFacilityDaysPriorToMaturityDate_f205a718-c798-42db-beda-fb95978c8398" xlink:href="band-20241231.xsd#band_LineOfCreditFacilityDaysPriorToMaturityDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_LineOfCreditFacilityDaysPriorToMaturityDate_f205a718-c798-42db-beda-fb95978c8398" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentCovenantLiquidityRequiredMinimum_b6717fec-c3a9-4941-9947-a9de52147afb" xlink:href="band-20241231.xsd#band_DebtInstrumentCovenantLiquidityRequiredMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentCovenantLiquidityRequiredMinimum_b6717fec-c3a9-4941-9947-a9de52147afb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentAdditionalBasisSpreadOnVariableRate_67605ab9-80c0-4e6f-9894-4ff945481ef0" xlink:href="band-20241231.xsd#band_DebtInstrumentAdditionalBasisSpreadOnVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentAdditionalBasisSpreadOnVariableRate_67605ab9-80c0-4e6f-9894-4ff945481ef0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_3d953756-4fc6-49c9-be1d-8c8a228d6f16" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_3d953756-4fc6-49c9-be1d-8c8a228d6f16" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_LineOfCreditFacilityCovenantConsecutiveQuarters_eb6b000c-dc8e-400f-b610-a00d414479a7" xlink:href="band-20241231.xsd#band_LineOfCreditFacilityCovenantConsecutiveQuarters"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_LineOfCreditFacilityCovenantConsecutiveQuarters_eb6b000c-dc8e-400f-b610-a00d414479a7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_5ac7fcce-445f-4dc1-a457-ee0250dfe3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_5ac7fcce-445f-4dc1-a457-ee0250dfe3e5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentCovenantLeverageRatioMaximumAllowed_b2a2642e-332b-432a-bd43-0f5620e287d4" xlink:href="band-20241231.xsd#band_DebtInstrumentCovenantLeverageRatioMaximumAllowed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentCovenantLeverageRatioMaximumAllowed_b2a2642e-332b-432a-bd43-0f5620e287d4" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleLiquidationPreferenceValue_97441885-5191-4454-93dd-565eaff45fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleLiquidationPreferenceValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_DebtInstrumentConvertibleLiquidationPreferenceValue_97441885-5191-4454-93dd-565eaff45fa5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentCovenantFixedChargeRatioMinimum_aad5693d-e7db-4ce9-9c14-581e33265f3a" xlink:href="band-20241231.xsd#band_DebtInstrumentCovenantFixedChargeRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentCovenantFixedChargeRatioMinimum_aad5693d-e7db-4ce9-9c14-581e33265f3a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentCovenantProFormaLeverageRatioMinimum_88fbe6a9-e259-4709-8c91-14b59744c664" xlink:href="band-20241231.xsd#band_DebtInstrumentCovenantProFormaLeverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentCovenantProFormaLeverageRatioMinimum_88fbe6a9-e259-4709-8c91-14b59744c664" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentCovenantProFormaTotalLeverageRatioMaximumAllowed_1f5f30d3-dcf9-4b25-b593-7a114a24d78c" xlink:href="band-20241231.xsd#band_DebtInstrumentCovenantProFormaTotalLeverageRatioMaximumAllowed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentCovenantProFormaTotalLeverageRatioMaximumAllowed_1f5f30d3-dcf9-4b25-b593-7a114a24d78c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentCollateralEquityInterestsPledgedPercentageOfCapitalStock_ddd26dae-096e-492a-bec6-87f8023deb49" xlink:href="band-20241231.xsd#band_DebtInstrumentCollateralEquityInterestsPledgedPercentageOfCapitalStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_band_DebtInstrumentCollateralEquityInterestsPledgedPercentageOfCapitalStock_ddd26dae-096e-492a-bec6-87f8023deb49" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_b77bbb7d-48c2-4389-b507-c99fc418c24d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_b77bbb7d-48c2-4389-b507-c99fc418c24d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_3dbf265c-6545-4668-bcea-63e0e0a16f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_LineOfCredit_3dbf265c-6545-4668-bcea-63e0e0a16f6f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_7922f5bf-d230-46db-97a6-17dcbf8eed7f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_04030b68-c28f-4d9f-95b1-2dc68b3d1f87" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_7922f5bf-d230-46db-97a6-17dcbf8eed7f" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/Debt2026ConvertibleNotesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#Debt2026ConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/Debt2026ConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_54add506-0b5d-4fec-b84d-06e2d49da8d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentTable_54add506-0b5d-4fec-b84d-06e2d49da8d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_b8fa43c1-f545-4935-b667-00e3ff9a2a75" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_54add506-0b5d-4fec-b84d-06e2d49da8d5" xlink:to="loc_us-gaap_DebtInstrumentAxis_b8fa43c1-f545-4935-b667-00e3ff9a2a75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b8fa43c1-f545-4935-b667-00e3ff9a2a75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_b8fa43c1-f545-4935-b667-00e3ff9a2a75" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b8fa43c1-f545-4935-b667-00e3ff9a2a75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6e4c5a2d-9e7f-4ede-824d-401aa30e307e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_b8fa43c1-f545-4935-b667-00e3ff9a2a75" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6e4c5a2d-9e7f-4ede-824d-401aa30e307e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_b4364b96-85a7-40eb-837c-1df2cb8d17c5" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_6e4c5a2d-9e7f-4ede-824d-401aa30e307e" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_b4364b96-85a7-40eb-837c-1df2cb8d17c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a168be99-ca67-480a-865a-a3ec89604570" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_54add506-0b5d-4fec-b84d-06e2d49da8d5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a168be99-ca67-480a-865a-a3ec89604570" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a168be99-ca67-480a-865a-a3ec89604570_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a168be99-ca67-480a-865a-a3ec89604570" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a168be99-ca67-480a-865a-a3ec89604570_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c2668991-a7f0-4229-b25a-d900516a0007" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a168be99-ca67-480a-865a-a3ec89604570" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c2668991-a7f0-4229-b25a-d900516a0007" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_489a0ca5-799c-423c-9988-2635cf61628c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c2668991-a7f0-4229-b25a-d900516a0007" xlink:to="loc_us-gaap_ConvertibleDebtMember_489a0ca5-799c-423c-9988-2635cf61628c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_49d41ab9-cdc6-4970-95f2-63f71bf3c866" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_54add506-0b5d-4fec-b84d-06e2d49da8d5" xlink:to="loc_us-gaap_StatementClassOfStockAxis_49d41ab9-cdc6-4970-95f2-63f71bf3c866" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_49d41ab9-cdc6-4970-95f2-63f71bf3c866_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_49d41ab9-cdc6-4970-95f2-63f71bf3c866" xlink:to="loc_us-gaap_ClassOfStockDomain_49d41ab9-cdc6-4970-95f2-63f71bf3c866_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6bb215f4-c157-4977-bc65-468621bf500d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_49d41ab9-cdc6-4970-95f2-63f71bf3c866" xlink:to="loc_us-gaap_ClassOfStockDomain_6bb215f4-c157-4977-bc65-468621bf500d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_2968553e-9b0e-4fec-9f1b-375940c013bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_6bb215f4-c157-4977-bc65-468621bf500d" xlink:to="loc_us-gaap_CommonClassAMember_2968553e-9b0e-4fec-9f1b-375940c013bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_713f60d3-f6bd-4321-ad9d-116f3ff05228" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_713f60d3-f6bd-4321-ad9d-116f3ff05228" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_6c3b5ad7-d4b9-415a-9a5c-e6e3a8743e98" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_6c3b5ad7-d4b9-415a-9a5c-e6e3a8743e98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet_8bdf13e1-fe53-44a8-91a0-51d245dd3936" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet_8bdf13e1-fe53-44a8-91a0-51d245dd3936" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_54b876f9-e961-49bd-922c-e472da3c3e24" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_54b876f9-e961-49bd-922c-e472da3c3e24" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_99b0469d-e42e-4c86-a643-11d3ceebbe6f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_99b0469d-e42e-4c86-a643-11d3ceebbe6f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_170d65d0-3b34-46aa-96b3-3e4529b2bb08" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_170d65d0-3b34-46aa-96b3-3e4529b2bb08" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_e559ede0-a8f2-469b-bf15-8fa3326010ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_e559ede0-a8f2-469b-bf15-8fa3326010ed" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_1f5ef068-507c-4637-9e5b-96380f3305f8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_1f5ef068-507c-4637-9e5b-96380f3305f8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_36b6de9b-eb4d-4376-9a8b-1293fa1e3ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_36b6de9b-eb4d-4376-9a8b-1293fa1e3ee1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_15910885-3cc7-4109-bd31-ca230f677c50" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_353f5607-259e-45f9-b5ad-084b5996d697" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_15910885-3cc7-4109-bd31-ca230f677c50" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/Debt2028ConvertibleNotesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#Debt2028ConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/Debt2028ConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_3a11c27a-ac87-4d1d-83a1-9146facc4c99" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_DebtInstrumentTable_3a11c27a-ac87-4d1d-83a1-9146facc4c99" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_57edc62d-f2ba-4edf-94c2-56af140c8996" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3a11c27a-ac87-4d1d-83a1-9146facc4c99" xlink:to="loc_us-gaap_DebtInstrumentAxis_57edc62d-f2ba-4edf-94c2-56af140c8996" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_57edc62d-f2ba-4edf-94c2-56af140c8996_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_57edc62d-f2ba-4edf-94c2-56af140c8996" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_57edc62d-f2ba-4edf-94c2-56af140c8996_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_214f8e7d-cfc1-4392-be87-d0e2d5eeec25" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_57edc62d-f2ba-4edf-94c2-56af140c8996" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_214f8e7d-cfc1-4392-be87-d0e2d5eeec25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_4c962ccb-fbe2-4035-803d-5d3276e1d1e3" xlink:href="band-20241231.xsd#band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_214f8e7d-cfc1-4392-be87-d0e2d5eeec25" xlink:to="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_4c962ccb-fbe2-4035-803d-5d3276e1d1e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_25a9aa20-862f-4561-8af3-e1073daabb77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3a11c27a-ac87-4d1d-83a1-9146facc4c99" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_25a9aa20-862f-4561-8af3-e1073daabb77" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_25a9aa20-862f-4561-8af3-e1073daabb77_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_25a9aa20-862f-4561-8af3-e1073daabb77" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_25a9aa20-862f-4561-8af3-e1073daabb77_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_add63552-e400-4e0e-bfae-0fa469f1f211" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_25a9aa20-862f-4561-8af3-e1073daabb77" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_add63552-e400-4e0e-bfae-0fa469f1f211" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_d8d3aa50-0087-47aa-9627-95fa24c31025" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_add63552-e400-4e0e-bfae-0fa469f1f211" xlink:to="loc_us-gaap_ConvertibleDebtMember_d8d3aa50-0087-47aa-9627-95fa24c31025" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_5e0f3d64-0b77-4645-90ea-47f4f5dff0ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3a11c27a-ac87-4d1d-83a1-9146facc4c99" xlink:to="loc_us-gaap_StatementClassOfStockAxis_5e0f3d64-0b77-4645-90ea-47f4f5dff0ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5e0f3d64-0b77-4645-90ea-47f4f5dff0ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5e0f3d64-0b77-4645-90ea-47f4f5dff0ee" xlink:to="loc_us-gaap_ClassOfStockDomain_5e0f3d64-0b77-4645-90ea-47f4f5dff0ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9ff556b5-a8ad-47d5-ab0e-0a0da5d13b2b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5e0f3d64-0b77-4645-90ea-47f4f5dff0ee" xlink:to="loc_us-gaap_ClassOfStockDomain_9ff556b5-a8ad-47d5-ab0e-0a0da5d13b2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_09eef388-05f2-453e-a24f-4e80ee817ce0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9ff556b5-a8ad-47d5-ab0e-0a0da5d13b2b" xlink:to="loc_us-gaap_CommonClassAMember_09eef388-05f2-453e-a24f-4e80ee817ce0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_f3ce0599-43f5-4ca1-8819-07dd5e61f578" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_f3ce0599-43f5-4ca1-8819-07dd5e61f578" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_74df5d65-5c34-42b2-a2fb-b32c6db91ab4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_74df5d65-5c34-42b2-a2fb-b32c6db91ab4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet_1051fa64-61f1-4106-8f02-cd9ebc703a70" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebtAndCapitalSecuritiesNet_1051fa64-61f1-4106-8f02-cd9ebc703a70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_cd8d2f62-8598-4dfc-98b1-37595aaf7515" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_cd8d2f62-8598-4dfc-98b1-37595aaf7515" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_56802375-3c9f-4615-9b25-c4d8f94a28f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_56802375-3c9f-4615-9b25-c4d8f94a28f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_7c616a05-f505-4b1c-95f8-04619ab6296e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_7c616a05-f505-4b1c-95f8-04619ab6296e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_be2efc5d-6e7a-409a-a589-df8f7949f73f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_570b5ddd-3cad-4f76-b8c1-c16312a42c83" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_be2efc5d-6e7a-409a-a589-df8f7949f73f" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/DebtOtherTermsoftheConvertibleNotesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#DebtOtherTermsoftheConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/DebtOtherTermsoftheConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_edbe32e1-3f17-444e-9fbc-e5c91820bded" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:to="loc_us-gaap_DebtInstrumentTable_edbe32e1-3f17-444e-9fbc-e5c91820bded" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_7f7f1fec-ff22-4a8b-a9e8-006b5e627698" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_edbe32e1-3f17-444e-9fbc-e5c91820bded" xlink:to="loc_us-gaap_DebtInstrumentAxis_7f7f1fec-ff22-4a8b-a9e8-006b5e627698" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7f7f1fec-ff22-4a8b-a9e8-006b5e627698_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_7f7f1fec-ff22-4a8b-a9e8-006b5e627698" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7f7f1fec-ff22-4a8b-a9e8-006b5e627698_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_da9e19fb-964c-433a-a7f5-36bae49d503b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_7f7f1fec-ff22-4a8b-a9e8-006b5e627698" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_da9e19fb-964c-433a-a7f5-36bae49d503b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_d89d5f95-1c4c-4331-80a3-986f3cdbf367" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da9e19fb-964c-433a-a7f5-36bae49d503b" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_d89d5f95-1c4c-4331-80a3-986f3cdbf367" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_d98f520c-bc4b-4895-bb48-7e1b074e39cf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_edbe32e1-3f17-444e-9fbc-e5c91820bded" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_d98f520c-bc4b-4895-bb48-7e1b074e39cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_d98f520c-bc4b-4895-bb48-7e1b074e39cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_d98f520c-bc4b-4895-bb48-7e1b074e39cf" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_d98f520c-bc4b-4895-bb48-7e1b074e39cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_02df3b9f-8129-4d43-8e8d-00c1dbe37b54" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_d98f520c-bc4b-4895-bb48-7e1b074e39cf" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_02df3b9f-8129-4d43-8e8d-00c1dbe37b54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_c4c41f47-fa4a-40e1-a80b-ab18c323cb82" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_02df3b9f-8129-4d43-8e8d-00c1dbe37b54" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_c4c41f47-fa4a-40e1-a80b-ab18c323cb82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a08a4d59-f209-48ab-a398-3fc8fd059c90" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_edbe32e1-3f17-444e-9fbc-e5c91820bded" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a08a4d59-f209-48ab-a398-3fc8fd059c90" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a08a4d59-f209-48ab-a398-3fc8fd059c90_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a08a4d59-f209-48ab-a398-3fc8fd059c90" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a08a4d59-f209-48ab-a398-3fc8fd059c90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b0c00110-2018-4f6f-9ead-73290c9d862c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a08a4d59-f209-48ab-a398-3fc8fd059c90" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b0c00110-2018-4f6f-9ead-73290c9d862c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_8acf34ed-12a6-47c1-855b-ef5f3546c8b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_b0c00110-2018-4f6f-9ead-73290c9d862c" xlink:to="loc_us-gaap_ConvertibleDebtMember_8acf34ed-12a6-47c1-855b-ef5f3546c8b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_00b58ce8-e9f4-46da-93bc-e2227bc1e11c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_edbe32e1-3f17-444e-9fbc-e5c91820bded" xlink:to="loc_us-gaap_StatementClassOfStockAxis_00b58ce8-e9f4-46da-93bc-e2227bc1e11c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_00b58ce8-e9f4-46da-93bc-e2227bc1e11c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_00b58ce8-e9f4-46da-93bc-e2227bc1e11c" xlink:to="loc_us-gaap_ClassOfStockDomain_00b58ce8-e9f4-46da-93bc-e2227bc1e11c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_1ddafe46-9cea-470d-b4a9-9a554ca0e7f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_00b58ce8-e9f4-46da-93bc-e2227bc1e11c" xlink:to="loc_us-gaap_ClassOfStockDomain_1ddafe46-9cea-470d-b4a9-9a554ca0e7f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_547e4980-f34d-48ce-8487-c0e059aec062" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_1ddafe46-9cea-470d-b4a9-9a554ca0e7f1" xlink:to="loc_us-gaap_CommonClassAMember_547e4980-f34d-48ce-8487-c0e059aec062" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentRedemptionPeriodTradingDaysToMaturity_1f547464-ba5c-428d-90cc-d88237905999" xlink:href="band-20241231.xsd#band_DebtInstrumentRedemptionPeriodTradingDaysToMaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:to="loc_band_DebtInstrumentRedemptionPeriodTradingDaysToMaturity_1f547464-ba5c-428d-90cc-d88237905999" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_b8677e5b-0817-4086-97e1-c8b9c775b7cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_b8677e5b-0817-4086-97e1-c8b9c775b7cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_db69cce4-e3fb-4983-8bf9-34e8f750f0da" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_db69cce4-e3fb-4983-8bf9-34e8f750f0da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_7a4033f1-9c21-48d1-8969-584dd053361e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_7a4033f1-9c21-48d1-8969-584dd053361e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_95ee4f45-8dfc-426e-bbc0-1d72b425d031" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e5ce419d-00c8-4546-985f-44d8e939b743" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_95ee4f45-8dfc-426e-bbc0-1d72b425d031" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/DebtScheduleofNetCarryingAmountofLiabilityComponentsofConvertibleNotesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#DebtScheduleofNetCarryingAmountofLiabilityComponentsofConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/DebtScheduleofNetCarryingAmountofLiabilityComponentsofConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_c7ccbfc2-cd31-4187-bf97-60b505c6fb7d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_5df4d649-5fdc-44d5-93f1-31868a14a10e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c7ccbfc2-cd31-4187-bf97-60b505c6fb7d" xlink:to="loc_us-gaap_DebtInstrumentTable_5df4d649-5fdc-44d5-93f1-31868a14a10e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_a3f00a7f-eae0-4b38-8195-89b4fac87c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_5df4d649-5fdc-44d5-93f1-31868a14a10e" xlink:to="loc_us-gaap_DebtInstrumentAxis_a3f00a7f-eae0-4b38-8195-89b4fac87c2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_a3f00a7f-eae0-4b38-8195-89b4fac87c2a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_a3f00a7f-eae0-4b38-8195-89b4fac87c2a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_a3f00a7f-eae0-4b38-8195-89b4fac87c2a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d7c200d0-e854-428b-8f6d-9fb93885c7d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_a3f00a7f-eae0-4b38-8195-89b4fac87c2a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d7c200d0-e854-428b-8f6d-9fb93885c7d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_d0db3af0-3ec4-40e9-9241-9231c3a23e41" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d7c200d0-e854-428b-8f6d-9fb93885c7d0" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_d0db3af0-3ec4-40e9-9241-9231c3a23e41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_839fda88-f84f-46e0-b38d-dc6ec9a5f191" xlink:href="band-20241231.xsd#band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d7c200d0-e854-428b-8f6d-9fb93885c7d0" xlink:to="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_839fda88-f84f-46e0-b38d-dc6ec9a5f191" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_4acbde42-798f-4a21-ad5a-e65b8e0f2d57" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_5df4d649-5fdc-44d5-93f1-31868a14a10e" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_4acbde42-798f-4a21-ad5a-e65b8e0f2d57" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_4acbde42-798f-4a21-ad5a-e65b8e0f2d57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4acbde42-798f-4a21-ad5a-e65b8e0f2d57" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_4acbde42-798f-4a21-ad5a-e65b8e0f2d57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_1be3bdc5-8b47-479e-9fe4-798ff4d5136d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4acbde42-798f-4a21-ad5a-e65b8e0f2d57" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_1be3bdc5-8b47-479e-9fe4-798ff4d5136d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_62310190-bfe8-4ea7-acf4-a9f560fb03f6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_1be3bdc5-8b47-479e-9fe4-798ff4d5136d" xlink:to="loc_us-gaap_ConvertibleDebtMember_62310190-bfe8-4ea7-acf4-a9f560fb03f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_8f3ffdb0-b7e1-4e5a-a982-51397e8f81d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c7ccbfc2-cd31-4187-bf97-60b505c6fb7d" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_8f3ffdb0-b7e1-4e5a-a982-51397e8f81d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_6991d7a1-1cab-42a2-9ea4-827d35f507b8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c7ccbfc2-cd31-4187-bf97-60b505c6fb7d" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_6991d7a1-1cab-42a2-9ea4-827d35f507b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_c997213c-9a93-43b8-8940-4b9f76da1924" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c7ccbfc2-cd31-4187-bf97-60b505c6fb7d" xlink:to="loc_us-gaap_LongTermDebt_c997213c-9a93-43b8-8940-4b9f76da1924" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/DebtScheduleofInterestExpenseRecognizedRelatedtoConvertibleNotesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#DebtScheduleofInterestExpenseRecognizedRelatedtoConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/DebtScheduleofInterestExpenseRecognizedRelatedtoConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_7080232b-fe75-42ac-9a62-a8a351ef3750" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_82421a13-f107-4cdd-977a-b6bf3c9f4638" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7080232b-fe75-42ac-9a62-a8a351ef3750" xlink:to="loc_us-gaap_DebtInstrumentTable_82421a13-f107-4cdd-977a-b6bf3c9f4638" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_169f19c8-54fc-4dbd-9aa2-814d8a084377" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_82421a13-f107-4cdd-977a-b6bf3c9f4638" xlink:to="loc_us-gaap_DebtInstrumentAxis_169f19c8-54fc-4dbd-9aa2-814d8a084377" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_169f19c8-54fc-4dbd-9aa2-814d8a084377_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_169f19c8-54fc-4dbd-9aa2-814d8a084377" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_169f19c8-54fc-4dbd-9aa2-814d8a084377_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_7c259d1a-82a4-48be-9330-0a2820e655e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_169f19c8-54fc-4dbd-9aa2-814d8a084377" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_7c259d1a-82a4-48be-9330-0a2820e655e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_853c8cfc-4064-4970-8ca0-7696012d35e1" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7c259d1a-82a4-48be-9330-0a2820e655e0" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_853c8cfc-4064-4970-8ca0-7696012d35e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_7278f5d4-7a4b-4df2-81ca-285b23c1d17a" xlink:href="band-20241231.xsd#band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_7c259d1a-82a4-48be-9330-0a2820e655e0" xlink:to="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_7278f5d4-7a4b-4df2-81ca-285b23c1d17a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_9944045d-4f12-44e5-9cb9-53e54e62d1e4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7080232b-fe75-42ac-9a62-a8a351ef3750" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_9944045d-4f12-44e5-9cb9-53e54e62d1e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_901bc9f3-28bf-4de7-9bc4-d2e809ab471a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7080232b-fe75-42ac-9a62-a8a351ef3750" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_901bc9f3-28bf-4de7-9bc4-d2e809ab471a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_0b80bd6f-fc7e-4998-890a-69a472761350" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7080232b-fe75-42ac-9a62-a8a351ef3750" xlink:to="loc_us-gaap_InterestExpenseDebt_0b80bd6f-fc7e-4998-890a-69a472761350" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/DebtScheduleofCostsIncurredforCappedCallsRelatedtoConvertibleNotesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#DebtScheduleofCostsIncurredforCappedCallsRelatedtoConvertibleNotesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/DebtScheduleofCostsIncurredforCappedCallsRelatedtoConvertibleNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_194c85cc-b17a-4901-a0f1-c18567457cb0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a41702f6-decb-4a31-8ffa-8a87f69283ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_194c85cc-b17a-4901-a0f1-c18567457cb0" xlink:to="loc_us-gaap_DebtInstrumentTable_a41702f6-decb-4a31-8ffa-8a87f69283ed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_3e9b64e5-2deb-467f-a8d4-8a2bfe93a58f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a41702f6-decb-4a31-8ffa-8a87f69283ed" xlink:to="loc_us-gaap_DebtInstrumentAxis_3e9b64e5-2deb-467f-a8d4-8a2bfe93a58f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_3e9b64e5-2deb-467f-a8d4-8a2bfe93a58f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_3e9b64e5-2deb-467f-a8d4-8a2bfe93a58f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_3e9b64e5-2deb-467f-a8d4-8a2bfe93a58f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_81593da9-1362-4304-abe7-f20dc7079723" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_3e9b64e5-2deb-467f-a8d4-8a2bfe93a58f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_81593da9-1362-4304-abe7-f20dc7079723" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_1dadecda-1920-4ed3-9d90-97c8c5ea22f9" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_81593da9-1362-4304-abe7-f20dc7079723" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_1dadecda-1920-4ed3-9d90-97c8c5ea22f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_d8a0ac4c-ce7a-40eb-b03d-0d16836c259a" xlink:href="band-20241231.xsd#band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_81593da9-1362-4304-abe7-f20dc7079723" xlink:to="loc_band_ZeroPointFiveZeroPercentConvertibleSeniorNotesDue2028Member_d8a0ac4c-ce7a-40eb-b03d-0d16836c259a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_950423a2-583c-4110-874a-3fc08933be3c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a41702f6-decb-4a31-8ffa-8a87f69283ed" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_950423a2-583c-4110-874a-3fc08933be3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_950423a2-583c-4110-874a-3fc08933be3c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_950423a2-583c-4110-874a-3fc08933be3c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_950423a2-583c-4110-874a-3fc08933be3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f38f593f-5b37-4219-bb76-6997e75e5354" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_950423a2-583c-4110-874a-3fc08933be3c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f38f593f-5b37-4219-bb76-6997e75e5354" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_494680b4-92ee-4fe4-ae1d-025b7772b00f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_f38f593f-5b37-4219-bb76-6997e75e5354" xlink:to="loc_us-gaap_ConvertibleDebtMember_494680b4-92ee-4fe4-ae1d-025b7772b00f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_c51ed3dd-fffc-4530-9536-4c9887370f8a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a41702f6-decb-4a31-8ffa-8a87f69283ed" xlink:to="loc_us-gaap_StatementClassOfStockAxis_c51ed3dd-fffc-4530-9536-4c9887370f8a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c51ed3dd-fffc-4530-9536-4c9887370f8a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c51ed3dd-fffc-4530-9536-4c9887370f8a" xlink:to="loc_us-gaap_ClassOfStockDomain_c51ed3dd-fffc-4530-9536-4c9887370f8a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d3637778-53d4-4089-8731-707671956427" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c51ed3dd-fffc-4530-9536-4c9887370f8a" xlink:to="loc_us-gaap_ClassOfStockDomain_d3637778-53d4-4089-8731-707671956427" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_671f9fc7-a234-4a3b-a191-62d972b35102" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d3637778-53d4-4089-8731-707671956427" xlink:to="loc_us-gaap_CommonClassAMember_671f9fc7-a234-4a3b-a191-62d972b35102" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentConvertibleInitialConversionStrikePrice_a1e1f2c4-0b77-4368-9eeb-2b02282728ae" xlink:href="band-20241231.xsd#band_DebtInstrumentConvertibleInitialConversionStrikePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_194c85cc-b17a-4901-a0f1-c18567457cb0" xlink:to="loc_band_DebtInstrumentConvertibleInitialConversionStrikePrice_a1e1f2c4-0b77-4368-9eeb-2b02282728ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentConvertibleInitialCapPrice_8b7eca2a-e615-4543-bfed-d626cce3e0f7" xlink:href="band-20241231.xsd#band_DebtInstrumentConvertibleInitialCapPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_194c85cc-b17a-4901-a0f1-c18567457cb0" xlink:to="loc_band_DebtInstrumentConvertibleInitialCapPrice_8b7eca2a-e615-4543-bfed-d626cce3e0f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CappedCallOptionIssuanceCost_b01bc408-ff0c-4728-aa84-646f56998c26" xlink:href="band-20241231.xsd#band_CappedCallOptionIssuanceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_194c85cc-b17a-4901-a0f1-c18567457cb0" xlink:to="loc_band_CappedCallOptionIssuanceCost_b01bc408-ff0c-4728-aa84-646f56998c26" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DebtInstrumentConvertibleConversionCappedCallShares_69471bc4-d400-4730-8e0c-07006f42f656" xlink:href="band-20241231.xsd#band_DebtInstrumentConvertibleConversionCappedCallShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_194c85cc-b17a-4901-a0f1-c18567457cb0" xlink:to="loc_band_DebtInstrumentConvertibleConversionCappedCallShares_69471bc4-d400-4730-8e0c-07006f42f656" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/GeographicInformationScheduleofRevenuebyGeographicAreaDetails" xlink:type="simple" xlink:href="band-20241231.xsd#GeographicInformationScheduleofRevenuebyGeographicAreaDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/GeographicInformationScheduleofRevenuebyGeographicAreaDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_2079ee37-1e10-40ff-9d7a-f5f1d465feef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_dfba72da-0d03-4445-af1d-d8c023abccfc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_2079ee37-1e10-40ff-9d7a-f5f1d465feef" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_dfba72da-0d03-4445-af1d-d8c023abccfc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_1678fb72-5c02-45d9-bce8-6471d16b29f7" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_dfba72da-0d03-4445-af1d-d8c023abccfc" xlink:to="loc_srt_StatementGeographicalAxis_1678fb72-5c02-45d9-bce8-6471d16b29f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_1678fb72-5c02-45d9-bce8-6471d16b29f7_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_1678fb72-5c02-45d9-bce8-6471d16b29f7" xlink:to="loc_srt_SegmentGeographicalDomain_1678fb72-5c02-45d9-bce8-6471d16b29f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_6561fa8d-b6e7-41b9-b0cb-0635af35d543" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_1678fb72-5c02-45d9-bce8-6471d16b29f7" xlink:to="loc_srt_SegmentGeographicalDomain_6561fa8d-b6e7-41b9-b0cb-0635af35d543" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_4f84c607-1b0d-481d-ae5e-b309590917ff" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_6561fa8d-b6e7-41b9-b0cb-0635af35d543" xlink:to="loc_country_US_4f84c607-1b0d-481d-ae5e-b309590917ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_b388f4d2-eceb-4a97-8213-9b53fe7d7fc4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_6561fa8d-b6e7-41b9-b0cb-0635af35d543" xlink:to="loc_us-gaap_NonUsMember_b388f4d2-eceb-4a97-8213-9b53fe7d7fc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_80fbc4b4-7614-42ea-9ea1-04c401be08ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_2079ee37-1e10-40ff-9d7a-f5f1d465feef" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_80fbc4b4-7614-42ea-9ea1-04c401be08ee" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/GeographicInformationScheduleofLongLivedAssetsbyGeographicAreaDetails" xlink:type="simple" xlink:href="band-20241231.xsd#GeographicInformationScheduleofLongLivedAssetsbyGeographicAreaDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/GeographicInformationScheduleofLongLivedAssetsbyGeographicAreaDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_8c590834-e574-4623-80f2-342bbf2e9172" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_1fb69bc4-1e9c-4a52-b207-724fe105c452" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_8c590834-e574-4623-80f2-342bbf2e9172" xlink:to="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_1fb69bc4-1e9c-4a52-b207-724fe105c452" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_0172975c-0b32-4f1f-8790-ba4deff7a1b9" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable_1fb69bc4-1e9c-4a52-b207-724fe105c452" xlink:to="loc_srt_StatementGeographicalAxis_0172975c-0b32-4f1f-8790-ba4deff7a1b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_0172975c-0b32-4f1f-8790-ba4deff7a1b9_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_0172975c-0b32-4f1f-8790-ba4deff7a1b9" xlink:to="loc_srt_SegmentGeographicalDomain_0172975c-0b32-4f1f-8790-ba4deff7a1b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_72d211eb-ff15-45c5-9a4f-9d54c1862323" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_0172975c-0b32-4f1f-8790-ba4deff7a1b9" xlink:to="loc_srt_SegmentGeographicalDomain_72d211eb-ff15-45c5-9a4f-9d54c1862323" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_f58bca1b-f014-4784-9952-e43485d97778" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_72d211eb-ff15-45c5-9a4f-9d54c1862323" xlink:to="loc_country_US_f58bca1b-f014-4784-9952-e43485d97778" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_7c7d1ce1-512e-4a1e-b481-2e0a98fdd5d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_72d211eb-ff15-45c5-9a4f-9d54c1862323" xlink:to="loc_us-gaap_NonUsMember_7c7d1ce1-512e-4a1e-b481-2e0a98fdd5d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncurrentAssets_7f12c9ee-f62a-448e-8dec-02ab1fa8d25c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems_8c590834-e574-4623-80f2-342bbf2e9172" xlink:to="loc_us-gaap_NoncurrentAssets_7f12c9ee-f62a-448e-8dec-02ab1fa8d25c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#StockholdersEquityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_eff6a255-9034-45cc-a6fa-a18a917dde4a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_eff6a255-9034-45cc-a6fa-a18a917dde4a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9892a464-239a-47a5-9f69-f61b4889b46f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_eff6a255-9034-45cc-a6fa-a18a917dde4a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9892a464-239a-47a5-9f69-f61b4889b46f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9892a464-239a-47a5-9f69-f61b4889b46f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9892a464-239a-47a5-9f69-f61b4889b46f" xlink:to="loc_us-gaap_ClassOfStockDomain_9892a464-239a-47a5-9f69-f61b4889b46f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8aa2f8fb-c990-4bdb-9dfc-f96f0452ee09" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9892a464-239a-47a5-9f69-f61b4889b46f" xlink:to="loc_us-gaap_ClassOfStockDomain_8aa2f8fb-c990-4bdb-9dfc-f96f0452ee09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_3f476ef4-adb2-4004-ac09-f0be47e5f00c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8aa2f8fb-c990-4bdb-9dfc-f96f0452ee09" xlink:to="loc_us-gaap_CommonClassAMember_3f476ef4-adb2-4004-ac09-f0be47e5f00c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_4ecc28cb-6c8e-4d5b-8868-9f7cb8b92ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8aa2f8fb-c990-4bdb-9dfc-f96f0452ee09" xlink:to="loc_us-gaap_CommonClassBMember_4ecc28cb-6c8e-4d5b-8868-9f7cb8b92ad2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_0e84f177-4e07-4913-9abe-f78eabfeabfb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_0e84f177-4e07-4913-9abe-f78eabfeabfb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_141e5318-de53-4977-b18f-21453003e8fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_141e5318-de53-4977-b18f-21453003e8fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_11d3d384-fee5-46be-948c-3b6009925012" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_11d3d384-fee5-46be-948c-3b6009925012" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_e7a8e808-b8b2-4bf1-b1d4-063811956685" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_PreferredStockSharesIssued_e7a8e808-b8b2-4bf1-b1d4-063811956685" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_440249f9-a010-4868-ab10-55143e5fa34d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_440249f9-a010-4868-ab10-55143e5fa34d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_49fb2307-caed-47d4-a696-0b719c27bccd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_49fb2307-caed-47d4-a696-0b719c27bccd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_8d37a882-3b93-4b42-b0e2-f9429f0fd4f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_8d37a882-3b93-4b42-b0e2-f9429f0fd4f7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CommonStockVotingRightsVotesPerShare_77828ce3-4c01-4bd8-ab51-975b39951ef5" xlink:href="band-20241231.xsd#band_CommonStockVotingRightsVotesPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_band_CommonStockVotingRightsVotesPerShare_77828ce3-4c01-4bd8-ab51-975b39951ef5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_e6437a40-8fdf-4b17-b850-b2572f2fb81d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_e8f51812-d8ed-4255-b711-aafc299e8bdc" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_e6437a40-8fdf-4b17-b850-b2572f2fb81d" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/StockholdersEquityScheduleofReservedSharesofCommonStockforIssuanceDetails" xlink:type="simple" xlink:href="band-20241231.xsd#StockholdersEquityScheduleofReservedSharesofCommonStockforIssuanceDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/StockholdersEquityScheduleofReservedSharesofCommonStockforIssuanceDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_739cd836-6194-4309-95e8-053845bc95d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_58d32a1e-eb14-4ea3-a7fc-945ac22b67d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_739cd836-6194-4309-95e8-053845bc95d6" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_58d32a1e-eb14-4ea3-a7fc-945ac22b67d1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_bea679a5-4429-4a10-acf8-d835c21b7fce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_58d32a1e-eb14-4ea3-a7fc-945ac22b67d1" xlink:to="loc_us-gaap_AwardTypeAxis_bea679a5-4429-4a10-acf8-d835c21b7fce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_bea679a5-4429-4a10-acf8-d835c21b7fce_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_bea679a5-4429-4a10-acf8-d835c21b7fce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_bea679a5-4429-4a10-acf8-d835c21b7fce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e81de4a-777c-4965-ae30-d46f3b55e0ea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_bea679a5-4429-4a10-acf8-d835c21b7fce" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e81de4a-777c-4965-ae30-d46f3b55e0ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7c00ce25-6d6a-424f-89ec-2037dad48f6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e81de4a-777c-4965-ae30-d46f3b55e0ea" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7c00ce25-6d6a-424f-89ec-2037dad48f6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_ba52e2ae-ddf9-4573-ae21-2ca6dbbea4e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e81de4a-777c-4965-ae30-d46f3b55e0ea" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_ba52e2ae-ddf9-4573-ae21-2ca6dbbea4e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_e13324cb-7212-4751-a70b-7892edf0fb77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e81de4a-777c-4965-ae30-d46f3b55e0ea" xlink:to="loc_us-gaap_StockCompensationPlanMember_e13324cb-7212-4751-a70b-7892edf0fb77" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_397e1ff9-6f5d-4985-8af9-8b910f1c703c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_739cd836-6194-4309-95e8-053845bc95d6" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_397e1ff9-6f5d-4985-8af9-8b910f1c703c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#StockBasedCompensationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/StockBasedCompensationAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50cbe99c-cf4d-44d8-8778-84d3a8eb29ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50cbe99c-cf4d-44d8-8778-84d3a8eb29ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_228176d3-0191-4b1f-a335-b1dd89bf804e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50cbe99c-cf4d-44d8-8778-84d3a8eb29ec" xlink:to="loc_us-gaap_PlanNameAxis_228176d3-0191-4b1f-a335-b1dd89bf804e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_228176d3-0191-4b1f-a335-b1dd89bf804e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_228176d3-0191-4b1f-a335-b1dd89bf804e" xlink:to="loc_us-gaap_PlanNameDomain_228176d3-0191-4b1f-a335-b1dd89bf804e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_056b42a0-0180-49ea-a6ee-d1047f5f889e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_228176d3-0191-4b1f-a335-b1dd89bf804e" xlink:to="loc_us-gaap_PlanNameDomain_056b42a0-0180-49ea-a6ee-d1047f5f889e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_StockOptionPlan2010Member_d18329d2-efd1-42af-99b3-a8b68a073498" xlink:href="band-20241231.xsd#band_StockOptionPlan2010Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_056b42a0-0180-49ea-a6ee-d1047f5f889e" xlink:to="loc_band_StockOptionPlan2010Member_d18329d2-efd1-42af-99b3-a8b68a073498" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_A2017EquityCompensationPlanMember_4237b6cc-9dea-44a4-955c-21f5dfd854c1" xlink:href="band-20241231.xsd#band_A2017EquityCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_056b42a0-0180-49ea-a6ee-d1047f5f889e" xlink:to="loc_band_A2017EquityCompensationPlanMember_4237b6cc-9dea-44a4-955c-21f5dfd854c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_1d4bff84-3be7-48f7-9703-85639b95f0ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_50cbe99c-cf4d-44d8-8778-84d3a8eb29ec" xlink:to="loc_us-gaap_AwardTypeAxis_1d4bff84-3be7-48f7-9703-85639b95f0ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1d4bff84-3be7-48f7-9703-85639b95f0ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_1d4bff84-3be7-48f7-9703-85639b95f0ae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1d4bff84-3be7-48f7-9703-85639b95f0ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_760ecee6-f9ab-4219-8dd3-bd2427102179" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_1d4bff84-3be7-48f7-9703-85639b95f0ae" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_760ecee6-f9ab-4219-8dd3-bd2427102179" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_96348bc0-3b65-4693-9534-62909a40459f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_760ecee6-f9ab-4219-8dd3-bd2427102179" xlink:to="loc_us-gaap_EmployeeStockOptionMember_96348bc0-3b65-4693-9534-62909a40459f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_6fa0074f-36ab-4309-8aa2-f8d3972bf523" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_760ecee6-f9ab-4219-8dd3-bd2427102179" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_6fa0074f-36ab-4309-8aa2-f8d3972bf523" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_7bb5b88c-f59d-4775-a3dd-1202ef8c5063" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_7bb5b88c-f59d-4775-a3dd-1202ef8c5063" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_1d066f77-ce63-4a49-ae6b-56e3541c2553" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_1d066f77-ce63-4a49-ae6b-56e3541c2553" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_CommonStockCapitalSharesReservedForFutureIssuancePercentIncrease_3f227962-1616-426d-95cd-8792ca12529a" xlink:href="band-20241231.xsd#band_CommonStockCapitalSharesReservedForFutureIssuancePercentIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_band_CommonStockCapitalSharesReservedForFutureIssuancePercentIncrease_3f227962-1616-426d-95cd-8792ca12529a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_2848ab69-ba44-4b77-85cb-c47f6d58d10e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_2848ab69-ba44-4b77-85cb-c47f6d58d10e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_46590c6c-b05c-44c4-8b85-aa76f43cb19b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_46590c6c-b05c-44c4-8b85-aa76f43cb19b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_37d02fde-9578-42f3-a998-11797112947a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_37d02fde-9578-42f3-a998-11797112947a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_94258e4a-ffa0-4a46-8012-dd634ae741e6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_94258e4a-ffa0-4a46-8012-dd634ae741e6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_9bab41e3-c879-4cb3-b9fb-78e2a6c3c23f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_9bab41e3-c879-4cb3-b9fb-78e2a6c3c23f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_40128f9f-576b-462d-a4bf-9f606486613e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_40128f9f-576b-462d-a4bf-9f606486613e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_fe7d15b7-49c5-4f62-986b-dc55ab778624" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87fa3327-c090-405a-b138-333bdc654ede" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_fe7d15b7-49c5-4f62-986b-dc55ab778624" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/StockBasedCompensationScheduleofRestrictedStockUnitActivityDetails" xlink:type="simple" xlink:href="band-20241231.xsd#StockBasedCompensationScheduleofRestrictedStockUnitActivityDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/StockBasedCompensationScheduleofRestrictedStockUnitActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cdfeafa0-7259-4931-bad4-21463fbb03b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9be689bb-aa62-47e9-afbd-ed913ded63b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cdfeafa0-7259-4931-bad4-21463fbb03b9" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9be689bb-aa62-47e9-afbd-ed913ded63b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_089c5283-c048-48dd-bcc4-e6320f964499" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9be689bb-aa62-47e9-afbd-ed913ded63b6" xlink:to="loc_us-gaap_AwardTypeAxis_089c5283-c048-48dd-bcc4-e6320f964499" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_089c5283-c048-48dd-bcc4-e6320f964499_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_089c5283-c048-48dd-bcc4-e6320f964499" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_089c5283-c048-48dd-bcc4-e6320f964499_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fefdedfe-b29d-4a5b-b6c1-c7a37c562b85" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_089c5283-c048-48dd-bcc4-e6320f964499" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fefdedfe-b29d-4a5b-b6c1-c7a37c562b85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_3779e07b-bcc3-4848-af68-fbe2352670b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fefdedfe-b29d-4a5b-b6c1-c7a37c562b85" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_3779e07b-bcc3-4848-af68-fbe2352670b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward_03475043-876c-47ff-a6bc-b8d3a6a9317e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cdfeafa0-7259-4931-bad4-21463fbb03b9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward_03475043-876c-47ff-a6bc-b8d3a6a9317e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_43bf58e3-9ea4-4932-8622-f30c49a9ede2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward_03475043-876c-47ff-a6bc-b8d3a6a9317e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_43bf58e3-9ea4-4932-8622-f30c49a9ede2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_a6da3e5c-d4f1-4b2e-9feb-6ef2e3a453b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward_03475043-876c-47ff-a6bc-b8d3a6a9317e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_a6da3e5c-d4f1-4b2e-9feb-6ef2e3a453b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_ec7eaec1-78d2-4b04-b11b-2b7c8f2edd35" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward_03475043-876c-47ff-a6bc-b8d3a6a9317e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_ec7eaec1-78d2-4b04-b11b-2b7c8f2edd35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_86874d9a-c013-4131-b585-469e8ce2a0c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfSharesRollForward_03475043-876c-47ff-a6bc-b8d3a6a9317e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_86874d9a-c013-4131-b585-469e8ce2a0c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_76f7d9b8-ff93-4b82-ab3f-1cba3397ca4a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cdfeafa0-7259-4931-bad4-21463fbb03b9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_8be0a1f2-a874-4703-9a99-1d4bd22f1ee9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_8be0a1f2-a874-4703-9a99-1d4bd22f1ee9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_61f62a4f-19df-49ea-b87f-92a3c76dc915" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_61f62a4f-19df-49ea-b87f-92a3c76dc915" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_2f818717-8ac0-4d16-b110-7db2430889cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_2f818717-8ac0-4d16-b110-7db2430889cd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_6960bcd1-ef00-4a1b-a3d0-f00eff94d66d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_6960bcd1-ef00-4a1b-a3d0-f00eff94d66d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3a1ca813-2413-4a09-b387-c4be6fc23c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_3412d4cd-303c-47c0-bd31-ebafbbcc1c77" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4118aae3-a5a4-4843-8757-67d1e9009a2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_3412d4cd-303c-47c0-bd31-ebafbbcc1c77" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/StockBasedCompensationScheduleofTotalStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="band-20241231.xsd#StockBasedCompensationScheduleofTotalStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/StockBasedCompensationScheduleofTotalStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5467997e-9da4-46ab-8a36-800313e46ee6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_532556a1-dcd4-4379-a011-3e0ff66a0a05" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5467997e-9da4-46ab-8a36-800313e46ee6" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_532556a1-dcd4-4379-a011-3e0ff66a0a05" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_7087aa13-5daf-4461-9ac8-7e71af1f7e81" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_532556a1-dcd4-4379-a011-3e0ff66a0a05" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_7087aa13-5daf-4461-9ac8-7e71af1f7e81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_7087aa13-5daf-4461-9ac8-7e71af1f7e81_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_7087aa13-5daf-4461-9ac8-7e71af1f7e81" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_7087aa13-5daf-4461-9ac8-7e71af1f7e81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_f219b0a8-1ba3-4d71-93fb-833fc7c5e99f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_7087aa13-5daf-4461-9ac8-7e71af1f7e81" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_f219b0a8-1ba3-4d71-93fb-833fc7c5e99f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_1fd1409f-acdf-400e-bab2-c299036050b8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f219b0a8-1ba3-4d71-93fb-833fc7c5e99f" xlink:to="loc_us-gaap_CostOfSalesMember_1fd1409f-acdf-400e-bab2-c299036050b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_4a835dc7-2755-483a-9fc2-efb1f8ece846" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f219b0a8-1ba3-4d71-93fb-833fc7c5e99f" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_4a835dc7-2755-483a-9fc2-efb1f8ece846" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_e61bff74-b93d-4082-82a0-ebc6b36b7c64" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f219b0a8-1ba3-4d71-93fb-833fc7c5e99f" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_e61bff74-b93d-4082-82a0-ebc6b36b7c64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_3f5489d6-1d51-41a8-b8a3-c35e8cdfe7d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f219b0a8-1ba3-4d71-93fb-833fc7c5e99f" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_3f5489d6-1d51-41a8-b8a3-c35e8cdfe7d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_e5f8f890-ec2d-4db4-a3fc-463a666c2757" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_5467997e-9da4-46ab-8a36-800313e46ee6" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_e5f8f890-ec2d-4db4-a3fc-463a666c2757" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="band-20241231.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/CommitmentsandContingenciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_301929f7-308e-4bbe-a3a2-e4994c6f784b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_f8d56449-aab2-46be-a882-3cfc87540e22" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_301929f7-308e-4bbe-a3a2-e4994c6f784b" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_f8d56449-aab2-46be-a882-3cfc87540e22" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_61e2944c-8233-4509-a2b9-fc277c29468c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_f8d56449-aab2-46be-a882-3cfc87540e22" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_61e2944c-8233-4509-a2b9-fc277c29468c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_61e2944c-8233-4509-a2b9-fc277c29468c_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_61e2944c-8233-4509-a2b9-fc277c29468c" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_61e2944c-8233-4509-a2b9-fc277c29468c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_8555de81-61b8-4573-99d5-c50dcc008713" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis_61e2944c-8233-4509-a2b9-fc277c29468c" xlink:to="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_8555de81-61b8-4573-99d5-c50dcc008713" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_OfficeSpaceMember_a6ed9d27-6043-4066-9ac4-e6f60158eb96" xlink:href="band-20241231.xsd#band_OfficeSpaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RealEstateAndAccumulatedDepreciationNameOfPropertyDomain_8555de81-61b8-4573-99d5-c50dcc008713" xlink:to="loc_band_OfficeSpaceMember_a6ed9d27-6043-4066-9ac4-e6f60158eb96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_6e93aa9e-f969-4cb3-8ae7-4687f98f7224" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_301929f7-308e-4bbe-a3a2-e4994c6f784b" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_6e93aa9e-f969-4cb3-8ae7-4687f98f7224" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount_7fe57408-67b3-4235-b997-37fbe2ac08c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_301929f7-308e-4bbe-a3a2-e4994c6f784b" xlink:to="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount_7fe57408-67b3-4235-b997-37fbe2ac08c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary_836aa1b1-1310-45cf-81e1-6f7bd9d6531c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_301929f7-308e-4bbe-a3a2-e4994c6f784b" xlink:to="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary_836aa1b1-1310-45cf-81e1-6f7bd9d6531c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/EmployeeBenefitPlansAdditionalInformationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#EmployeeBenefitPlansAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/EmployeeBenefitPlansAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c625ff26-33a3-4033-b55c-f84a931bc0cf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c625ff26-33a3-4033-b55c-f84a931bc0cf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_95b8062f-ca9d-4b20-accd-bc3b62a9ff42" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_c625ff26-33a3-4033-b55c-f84a931bc0cf" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_95b8062f-ca9d-4b20-accd-bc3b62a9ff42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_95b8062f-ca9d-4b20-accd-bc3b62a9ff42_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_95b8062f-ca9d-4b20-accd-bc3b62a9ff42" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_95b8062f-ca9d-4b20-accd-bc3b62a9ff42_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_bdd0636a-c9b9-49fe-8c57-0f3682d46ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_95b8062f-ca9d-4b20-accd-bc3b62a9ff42" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_bdd0636a-c9b9-49fe-8c57-0f3682d46ea3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_InsuranceCompaniesMember_eb16472a-185f-4a1e-a38b-d73a4ee1545e" xlink:href="band-20241231.xsd#band_InsuranceCompaniesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_bdd0636a-c9b9-49fe-8c57-0f3682d46ea3" xlink:to="loc_band_InsuranceCompaniesMember_eb16472a-185f-4a1e-a38b-d73a4ee1545e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_26768c9d-e390-4a4b-8717-3bc5957f9ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_26768c9d-e390-4a4b-8717-3bc5957f9ff8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent_7858d9da-3aa2-4cea-8d7a-09105b64c3b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:to="loc_us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent_7858d9da-3aa2-4cea-8d7a-09105b64c3b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditImmediateRecognitionOfActuarialGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleList_5803a5e8-90fa-4320-bb5b-5a311ee97638" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditImmediateRecognitionOfActuarialGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditImmediateRecognitionOfActuarialGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleList_5803a5e8-90fa-4320-bb5b-5a311ee97638" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_c151786f-a559-4425-8a73-e587f44fd4b3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_c151786f-a559-4425-8a73-e587f44fd4b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_12191ca1-67b9-4d9d-9b4b-fa78e4f957bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_3629cee8-07cc-4f54-b489-a7f5497d4f95" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_12191ca1-67b9-4d9d-9b4b-fa78e4f957bd" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/IncomeTaxesAdditionalInformationDetails" xlink:type="simple" xlink:href="band-20241231.xsd#IncomeTaxesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/IncomeTaxesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_2489167d-4e52-4fb5-bc9c-dd7a6e98527c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_2489167d-4e52-4fb5-bc9c-dd7a6e98527c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_a05728ac-c91c-4f88-a3a7-4489b304b6d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_2489167d-4e52-4fb5-bc9c-dd7a6e98527c" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_a05728ac-c91c-4f88-a3a7-4489b304b6d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_a05728ac-c91c-4f88-a3a7-4489b304b6d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_a05728ac-c91c-4f88-a3a7-4489b304b6d8" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_a05728ac-c91c-4f88-a3a7-4489b304b6d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_9a1bb82f-ad12-4349-803f-1a2f1ab628ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_a05728ac-c91c-4f88-a3a7-4489b304b6d8" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_9a1bb82f-ad12-4349-803f-1a2f1ab628ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalMinistryOfFinanceGermanyMember_ba7bba58-db3b-4488-863e-52efb3cada94" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FederalMinistryOfFinanceGermanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_9a1bb82f-ad12-4349-803f-1a2f1ab628ac" xlink:to="loc_us-gaap_FederalMinistryOfFinanceGermanyMember_ba7bba58-db3b-4488-863e-52efb3cada94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxAndCustomsAdministrationNetherlandsMember_1aa7b5a2-0130-4018-ad8a-bf1a190ae84c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxAndCustomsAdministrationNetherlandsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_9a1bb82f-ad12-4349-803f-1a2f1ab628ac" xlink:to="loc_us-gaap_TaxAndCustomsAdministrationNetherlandsMember_1aa7b5a2-0130-4018-ad8a-bf1a190ae84c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_fad3f53a-3b56-4ea7-abff-397b2b802c67" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_9a1bb82f-ad12-4349-803f-1a2f1ab628ac" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_fad3f53a-3b56-4ea7-abff-397b2b802c67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_ceaa4715-2d03-44d3-b1a5-11cd3a768c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_ceaa4715-2d03-44d3-b1a5-11cd3a768c2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossAttributableToParent_8b1b5cca-8886-426a-b7f3-0d143ad1d3ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_IncomeLossAttributableToParent_8b1b5cca-8886-426a-b7f3-0d143ad1d3ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_917fed24-dc5c-4f66-abe8-10256ecef59c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_917fed24-dc5c-4f66-abe8-10256ecef59c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_97efb120-b7a2-4d14-ba5c-f88d12ff0c43" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_OperatingLossCarryforwards_97efb120-b7a2-4d14-ba5c-f88d12ff0c43" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_0f42e67b-3906-4f9f-a173-3cf1294e44de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxCreditCarryforwardAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_0f42e67b-3906-4f9f-a173-3cf1294e44de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_c0a0c541-f67d-450a-b8cd-0d34739b5379" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_c0a0c541-f67d-450a-b8cd-0d34739b5379" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_371e35ca-a47d-4350-b94d-de495def2ce1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_1aaae21d-ba56-46c3-aac4-adec7cfe1b57" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_371e35ca-a47d-4350-b94d-de495def2ce1" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/BasicandDilutedLossIncomeperCommonShareScheduleofAntidilutiveCommonSharesExcludedfromCalculationofDilutedNetLossIncomeDetails" xlink:type="simple" xlink:href="band-20241231.xsd#BasicandDilutedLossIncomeperCommonShareScheduleofAntidilutiveCommonSharesExcludedfromCalculationofDilutedNetLossIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/BasicandDilutedLossIncomeperCommonShareScheduleofAntidilutiveCommonSharesExcludedfromCalculationofDilutedNetLossIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_46b5f6ab-1b71-4214-9b46-1cdd2a9a7808" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_1112d5f5-86fb-4606-9334-0a53395ddd8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_46b5f6ab-1b71-4214-9b46-1cdd2a9a7808" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_1112d5f5-86fb-4606-9334-0a53395ddd8c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ae297ac0-17bd-4395-8976-a2beca3d0aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_1112d5f5-86fb-4606-9334-0a53395ddd8c" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ae297ac0-17bd-4395-8976-a2beca3d0aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ae297ac0-17bd-4395-8976-a2beca3d0aa8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ae297ac0-17bd-4395-8976-a2beca3d0aa8" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_ae297ac0-17bd-4395-8976-a2beca3d0aa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c38ecf08-f8b9-4cee-bd5e-04eb084044fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_ae297ac0-17bd-4395-8976-a2beca3d0aa8" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c38ecf08-f8b9-4cee-bd5e-04eb084044fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_ed2e7992-a0ed-4494-b4fb-2585c3b89347" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c38ecf08-f8b9-4cee-bd5e-04eb084044fe" xlink:to="loc_us-gaap_EmployeeStockOptionMember_ed2e7992-a0ed-4494-b4fb-2585c3b89347" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_7c88724d-4a11-4c00-83c5-8d64c4560c9f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c38ecf08-f8b9-4cee-bd5e-04eb084044fe" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_7c88724d-4a11-4c00-83c5-8d64c4560c9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_a9f93ab3-236e-40d5-9fff-938ce6ffa540" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c38ecf08-f8b9-4cee-bd5e-04eb084044fe" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_a9f93ab3-236e-40d5-9fff-938ce6ffa540" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_0ed1b06b-bb6d-461e-89fa-11f8d186b5b4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_46b5f6ab-1b71-4214-9b46-1cdd2a9a7808" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_0ed1b06b-bb6d-461e-89fa-11f8d186b5b4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.bandwidth.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="band-20241231.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.bandwidth.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_e2b98161-d980-49fd-94c0-dfd4ba9f7ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_98eee046-de37-43fe-b39d-bdf524d47a9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_e2b98161-d980-49fd-94c0-dfd4ba9f7ca2" xlink:to="loc_us-gaap_SubsequentEventTable_98eee046-de37-43fe-b39d-bdf524d47a9e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_6ada1385-ad96-4235-a048-7facb82f4405" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_98eee046-de37-43fe-b39d-bdf524d47a9e" xlink:to="loc_us-gaap_DebtInstrumentAxis_6ada1385-ad96-4235-a048-7facb82f4405" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6ada1385-ad96-4235-a048-7facb82f4405_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_6ada1385-ad96-4235-a048-7facb82f4405" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6ada1385-ad96-4235-a048-7facb82f4405_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_eb9bb98a-9baa-4206-bd48-babeb945e476" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_6ada1385-ad96-4235-a048-7facb82f4405" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_eb9bb98a-9baa-4206-bd48-babeb945e476" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_5bbd7054-8e14-4fd8-b3b1-d1ca0809320b" xlink:href="band-20241231.xsd#band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_eb9bb98a-9baa-4206-bd48-babeb945e476" xlink:to="loc_band_ZeroPointTwoFivePercentConvertibleSeniorNotesDue2026Member_5bbd7054-8e14-4fd8-b3b1-d1ca0809320b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_2ef8eb25-de57-48b9-9ca0-ce268f0d72e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_98eee046-de37-43fe-b39d-bdf524d47a9e" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_2ef8eb25-de57-48b9-9ca0-ce268f0d72e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_2ef8eb25-de57-48b9-9ca0-ce268f0d72e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2ef8eb25-de57-48b9-9ca0-ce268f0d72e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_2ef8eb25-de57-48b9-9ca0-ce268f0d72e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_55bcb9ed-e788-459a-835f-fb8e8acd8a40" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2ef8eb25-de57-48b9-9ca0-ce268f0d72e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_55bcb9ed-e788-459a-835f-fb8e8acd8a40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_25df6358-2b91-4e2e-a3a0-2b70545f9d21" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_55bcb9ed-e788-459a-835f-fb8e8acd8a40" xlink:to="loc_us-gaap_ConvertibleDebtMember_25df6358-2b91-4e2e-a3a0-2b70545f9d21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_215b3e80-5e2c-490c-bbf9-62a8b43b1fbc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_98eee046-de37-43fe-b39d-bdf524d47a9e" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_215b3e80-5e2c-490c-bbf9-62a8b43b1fbc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_215b3e80-5e2c-490c-bbf9-62a8b43b1fbc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_215b3e80-5e2c-490c-bbf9-62a8b43b1fbc" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_215b3e80-5e2c-490c-bbf9-62a8b43b1fbc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_d99376f8-55d4-435a-84e1-012f1a3786a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_215b3e80-5e2c-490c-bbf9-62a8b43b1fbc" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_d99376f8-55d4-435a-84e1-012f1a3786a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_4ad08990-7c32-4d79-bc70-dbb2d902fcea" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_d99376f8-55d4-435a-84e1-012f1a3786a4" xlink:to="loc_us-gaap_SubsequentEventMember_4ad08990-7c32-4d79-bc70-dbb2d902fcea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_9ca574a5-9c8f-4732-95ae-0444f68987af" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_98eee046-de37-43fe-b39d-bdf524d47a9e" xlink:to="loc_srt_StatementScenarioAxis_9ca574a5-9c8f-4732-95ae-0444f68987af" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_9ca574a5-9c8f-4732-95ae-0444f68987af_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_9ca574a5-9c8f-4732-95ae-0444f68987af" xlink:to="loc_srt_ScenarioUnspecifiedDomain_9ca574a5-9c8f-4732-95ae-0444f68987af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_68befcb2-6690-4e09-9519-fdb53066ff86" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_9ca574a5-9c8f-4732-95ae-0444f68987af" xlink:to="loc_srt_ScenarioUnspecifiedDomain_68befcb2-6690-4e09-9519-fdb53066ff86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_64108aca-a8ed-4fb6-89ef-d3c37e6a240c" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_68befcb2-6690-4e09-9519-fdb53066ff86" xlink:to="loc_srt_ScenarioForecastMember_64108aca-a8ed-4fb6-89ef-d3c37e6a240c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_a1be0bfd-94ce-4ccd-92b6-3a1fc43b8223" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e2b98161-d980-49fd-94c0-dfd4ba9f7ca2" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_a1be0bfd-94ce-4ccd-92b6-3a1fc43b8223" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_896358af-7c6c-472f-a082-b4698443d408" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e2b98161-d980-49fd-94c0-dfd4ba9f7ca2" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_896358af-7c6c-472f-a082-b4698443d408" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_ad03c86b-51e3-477b-bbf7-f2913154609b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e2b98161-d980-49fd-94c0-dfd4ba9f7ca2" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_ad03c86b-51e3-477b-bbf7-f2913154609b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_b3b03d51-db3b-49e4-8ca0-447b5bfae7a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e2b98161-d980-49fd-94c0-dfd4ba9f7ca2" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_b3b03d51-db3b-49e4-8ca0-447b5bfae7a9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-roles-2024.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:type="arc" order="101"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_KadeRossMember_d20fa188-cd1f-4f19-9dc2-99bed7e38860" xlink:href="band-20241231.xsd#band_KadeRossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_band_KadeRossMember_d20fa188-cd1f-4f19-9dc2-99bed7e38860" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_band_DarylE.RaifordMember_bea4fe51-f6a6-4343-89cf-daecf9825d7e" xlink:href="band-20241231.xsd#band_DarylE.RaifordMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_band_DarylE.RaifordMember_bea4fe51-f6a6-4343-89cf-daecf9825d7e" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
