    <SEC-DOCUMENT>0001057352-21-000059-index.html : 20210419
    <SEC-HEADER>0001057352-21-000059.hdr.sgml : 20210419
    <ACCEPTANCE-DATETIME>20210419161458
    ACCESSION NUMBER:		0001057352-21-000059
    CONFORMED SUBMISSION TYPE:	DEF 14A
    PUBLIC DOCUMENT COUNT:		14
    CONFORMED PERIOD OF REPORT:	20210602
    FILED AS OF DATE:		20210419
    DATE AS OF CHANGE:		20210419

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			COSTAR GROUP, INC.
    		CENTRAL INDEX KEY:			0001057352
    		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-BUSINESS SERVICES, NEC [7389]
    		IRS NUMBER:				522091509
    		STATE OF INCORPORATION:			DE
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		DEF 14A
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-24531
    		FILM NUMBER:		21834771

    	BUSINESS ADDRESS:
    		STREET 1:		1331 L STREET, NW
    		CITY:			WASHINGTON
    		STATE:			DC
    		ZIP:			20005
    		BUSINESS PHONE:		2023466500

    	MAIL ADDRESS:
    		STREET 1:		1331 L STREET, NW
    		CITY:			WASHINGTON
    		STATE:			DC
    		ZIP:			20005

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	COSTAR GROUP INC
    		DATE OF NAME CHANGE:	19990805
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>DEF 14A
    <SEQUENCE>1
    <FILENAME>a2021proxystatement-def14a.htm
    <DESCRIPTION>DEF 14A
    <TEXT>
    Document 1 - file: a2021proxystatement-def14a.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>2
    <FILENAME>a20200310124736a031.jpg
    <TEXT>
    Document 2 - file: a20200310124736a031.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>3
    <FILENAME>a3a041.jpg
    <TEXT>
    Document 3 - file: a3a041.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>4
    <FILENAME>acsignaturea041.jpg
    <TEXT>
    Document 4 - file: acsignaturea041.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>5
    <FILENAME>boardcomposition1.jpg
    <TEXT>
    Document 5 - file: boardcomposition1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>6
    <FILENAME>card11.jpg
    <TEXT>
    Document 6 - file: card11.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>7
    <FILENAME>card21.jpg
    <TEXT>
    Document 7 - file: card21.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>8
    <FILENAME>ebitda1.jpg
    <TEXT>
    Document 8 - file: ebitda1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>9
    <FILENAME>horizonchart-20211.jpg
    <TEXT>
    Document 9 - file: horizonchart-20211.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>10
    <FILENAME>netincome1.jpg
    <TEXT>
    Document 10 - file: netincome1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>11
    <FILENAME>operating1.jpg
    <TEXT>
    Document 11 - file: operating1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>12
    <FILENAME>pie11.jpg
    <TEXT>
    Document 12 - file: pie11.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>13
    <FILENAME>pie21.jpg
    <TEXT>
    Document 13 - file: pie21.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>14
    <FILENAME>variablepaycharta031.jpg
    <TEXT>
    Document 14 - file: variablepaycharta031.jpg

    </DOCUMENT>
    </SEC-DOCUMENT>