<SEC-DOCUMENT>0001842718-23-000025.txt : 20230418
<SEC-HEADER>0001842718-23-000025.hdr.sgml : 20230418
<ACCEPTANCE-DATETIME>20230418163422
ACCESSION NUMBER:		0001842718-23-000025
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20230403
FILED AS OF DATE:		20230418
DATE AS OF CHANGE:		20230418

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SUKUMARAN ANIL
		CENTRAL INDEX KEY:			0001915719

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-40557
		FILM NUMBER:		23827267

	MAIL ADDRESS:	
		STREET 1:		99 WALL STREET, #1950
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10005

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			INTEGRAL AD SCIENCE HOLDING CORP.
		CENTRAL INDEX KEY:			0001842718
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMPUTER PROGRAMMING, DATA PROCESSING, ETC. [7370]
		IRS NUMBER:				830731995
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		99 WALL STREET
		STREET 2:		#1950
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10005
		BUSINESS PHONE:		(646) 278-4871

	MAIL ADDRESS:	
		STREET 1:		99 WALL STREET
		STREET 2:		#1950
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10005

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	INTEGRAL AD SCIENCE HOLDING LLC
		DATE OF NAME CHANGE:	20210301

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	KAVACHA TOPCO, LLC
		DATE OF NAME CHANGE:	20210127
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_168185004739442.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0407</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-04-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001842718</issuerCik>
        <issuerName>INTEGRAL AD SCIENCE HOLDING CORP.</issuerName>
        <issuerTradingSymbol>IAS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001915719</rptOwnerCik>
            <rptOwnerName>SUKUMARAN ANIL</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O INTEGRAL AD SCIENCE HOLDING CORP.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NOT APPLICABLE</rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Accounting Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $0.001 par value</value>
            </securityTitle>
            <transactionDate>
                <value>2023-04-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>35039</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>90488</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Anil Sukumaran</signatureName>
        <signatureDate>2023-04-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
