<SEC-DOCUMENT>0001488139-21-000049.txt : 20210430
<SEC-HEADER>0001488139-21-000049.hdr.sgml : 20210430
<ACCEPTANCE-DATETIME>20210430161821
ACCESSION NUMBER:		0001488139-21-000049
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20210426
FILED AS OF DATE:		20210430
DATE AS OF CHANGE:		20210430

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Todd Lauren
		CENTRAL INDEX KEY:			0001857764

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34811
		FILM NUMBER:		21878317

	MAIL ADDRESS:	
		STREET 1:		C/O AMERESCO, INC.
		STREET 2:		111 SPEEN STREET, STE. 401
		CITY:			FRAMINGHAM
		STATE:			MA
		ZIP:			01701-3812

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Ameresco, Inc.
		CENTRAL INDEX KEY:			0001488139
		STANDARD INDUSTRIAL CLASSIFICATION:	CONSTRUCTION SPECIAL TRADE CONTRACTORS [1700]
		IRS NUMBER:				043512838
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		111 SPEEN STREET
		CITY:			FRAMINGHAM
		STATE:			MA
		ZIP:			01701
		BUSINESS PHONE:		508-661-2200

	MAIL ADDRESS:	
		STREET 1:		111 SPEEN STREET
		CITY:			FRAMINGHAM
		STATE:			MA
		ZIP:			01701
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>wf-form3_161981386427851.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2021-04-26</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001488139</issuerCik>
        <issuerName>Ameresco, Inc.</issuerName>
        <issuerTradingSymbol>AMRC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001857764</rptOwnerCik>
            <rptOwnerName>Todd Lauren</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O AMERESCO, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>111 SPEEN STREET, STE. 401</rptOwnerStreet2>
            <rptOwnerCity>FRAMINGHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01701-3812</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP - HR and Operations</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to purchase)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>43.0</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2031-03-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to purchase)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.05</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2028-03-07</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Of the shares subject to the option, 20% vest on March 5, 2022, and the remainder vest in four equal installments on each of the subsequent four anniversaries of such date.</footnote>
        <footnote id="F2">Of the shares subject to the option, 3,000 shares vested on March 8, 2021, and the remainder vest in two equal installments on each of the subsequent four anniversaries of such date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ David J. Corrsin, attorney-in-fact</signatureName>
        <signatureDate>2021-04-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
