content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
    <headerData>
      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001955607</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0001842718</issuerCik>
        <issuerName>INTEGRAL AD SCIENCE HOLDING CORP.</issuerName>
        <secFileNumber>001-40557</secFileNumber>
        <issuerAddress>
          <com:street1>99 WALL STREET</com:street1>
          <com:street2>#1950</com:street2>
          <com:city>NEW YORK</com:city>
          <com:stateOrCountry>NY</com:stateOrCountry>
          <com:zipCode>10005</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>(646) 278-4871</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>SECOR TANIA</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Officer</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>8929</noOfUnitsSold>
        <aggregateMarketValue>86708.63</aggregateMarketValue>
        <noOfUnitsOutstanding>159520093</noOfUnitsOutstanding>
        <approxSaleDate>03/08/2024</approxSaleDate>
        <securitiesExchangeName>NASDAQ</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>03/05/2024</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>8929</amountOfSecuritiesAcquired>
        <paymentDate>03/05/2024</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Tania R. Secor</name>
          <address>
            <com:street1>12 E 49th Street</com:street1>
            <com:street2>20th Floor</com:street2>
            <com:city>New York</com:city>
            <com:stateOrCountry>NY</com:stateOrCountry>
            <com:zipCode>10017</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>12/08/2023</saleDate>
        <amountOfSecuritiesSold>38394</amountOfSecuritiesSold>
        <grossProceeds>536264.36</grossProceeds>
      </securitiesSoldInPast3Months>
      <securitiesSoldInPast3Months>
        <sellerDetails>
          <name>Tania R. Secor</name>
          <address>
            <com:street1>12 E 49th Street</com:street1>
            <com:street2>20th Floor</com:street2>
            <com:city>New York</com:city>
            <com:stateOrCountry>NY</com:stateOrCountry>
            <com:zipCode>10017</com:zipCode>
          </address>
        </sellerDetails>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <saleDate>03/06/2024</saleDate>
        <amountOfSecuritiesSold>6570</amountOfSecuritiesSold>
        <grossProceeds>63764.48</grossProceeds>
      </securitiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>03/08/2024</noticeDate>
        <signature>/s/ Jodi Disselkamp, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Tania R. Secor</signature>
      </noticeSignature>
    </formData>
  </edgarSubmission>
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text: 144
  0001955607
  XXXXXXXX
  LIVE
  0001842718
  INTEGRAL AD SCIENCE HOLDING CORP.
  001-40557
  99 WALL STREET
  #1950
  NEW YORK
  NY
  10005
  (646) 278-4871
  SECOR TANIA
  Officer
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  8929
  86708.63
  159520093
  03/08/2024
  NASDAQ
  Common
  03/05/2024
  Restricted Stock Vesting
  Issuer
  N
  8929
  03/05/2024
  Compensation
  N
  Tania R. Secor
  12 E 49th Street
  20th Floor
  New York
  NY
  10017
  Common
  12/08/2023
  38394
  536264.36
  Tania R. Secor
  12 E 49th Street
  20th Floor
  New York
  NY
  10017
  Common
  03/06/2024
  6570
  63764.48
  03/08/2024
  /s/ Jodi Disselkamp, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Tania R. Secor