<SEC-DOCUMENT>0001488139-18-000076.txt : 20181005
<SEC-HEADER>0001488139-18-000076.hdr.sgml : 20181005
<ACCEPTANCE-DATETIME>20181005163240
ACCESSION NUMBER:		0001488139-18-000076
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20181001
FILED AS OF DATE:		20181005
DATE AS OF CHANGE:		20181005

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Chiplock Mark
		CENTRAL INDEX KEY:			0001755243

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34811
		FILM NUMBER:		181110869

	MAIL ADDRESS:	
		STREET 1:		C/O AMERESCO, INC.
		STREET 2:		111 SPEEN STREET, SUITE 410
		CITY:			FRAMINGHAM
		STATE:			MA
		ZIP:			01701

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_153877140775196.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2018-10-01</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001755243</rptOwnerCik>
            <rptOwnerName>Chiplock Mark</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>111 SPEEN STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 410</rptOwnerStreet2>
            <rptOwnerCity>FRAMINGHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President &amp; CFO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to purchase)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.79</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2024-07-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>21500.0</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>2018-03-07</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Of the shares subject to this option, 16,500 were vested as of the date hereof and the remainder will vest on July 23, 2019.</footnote>
        <footnote id="F2">Of the shares subject to the option, 20% vest on March 8, 2019, and the remainder vest in four equal installments on each of the subsequent four anniversaries of such date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Mark Chiplock</signatureName>
        <signatureDate>2018-10-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
