    <SEC-DOCUMENT>0001057352-19-000049-index.html : 20190424
    <SEC-HEADER>0001057352-19-000049.hdr.sgml : 20190424
    <ACCEPTANCE-DATETIME>20190423184419
    ACCESSION NUMBER:		0001057352-19-000049
    CONFORMED SUBMISSION TYPE:	DEF 14A
    PUBLIC DOCUMENT COUNT:		13
    CONFORMED PERIOD OF REPORT:	20190605
    FILED AS OF DATE:		20190424
    DATE AS OF CHANGE:		20190423
    EFFECTIVENESS DATE:		20190424

    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:		19762365

    	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
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>DEF 14A
    <SEQUENCE>1
    <FILENAME>a2019proxystatement.htm
    <DESCRIPTION>DEF 14A
    <TEXT>
    Document 1 - file: a2019proxystatement.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>2
    <FILENAME>a3a01.jpg
    <TEXT>
    Document 2 - file: a3a01.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>3
    <FILENAME>acsignaturea02.jpg
    <TEXT>
    Document 3 - file: acsignaturea02.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>4
    <FILENAME>card1.jpg
    <TEXT>
    Document 4 - file: card1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>5
    <FILENAME>card2.jpg
    <TEXT>
    Document 5 - file: card2.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>6
    <FILENAME>ebitdaa03.jpg
    <TEXT>
    Document 6 - file: ebitdaa03.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>7
    <FILENAME>horizona01.jpg
    <TEXT>
    Document 7 - file: horizona01.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>8
    <FILENAME>jcsignaturea02.jpg
    <TEXT>
    Document 8 - file: jcsignaturea02.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>9
    <FILENAME>netincomea01.jpg
    <TEXT>
    Document 9 - file: netincomea01.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>10
    <FILENAME>operatingrevenuea03.jpg
    <TEXT>
    Document 10 - file: operatingrevenuea03.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>11
    <FILENAME>pie1.jpg
    <TEXT>
    Document 11 - file: pie1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>12
    <FILENAME>pie2v2.jpg
    <TEXT>
    Document 12 - file: pie2v2.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>13
    <FILENAME>variablepaycharta01.jpg
    <TEXT>
    Document 13 - file: variablepaycharta01.jpg

    </DOCUMENT>
    </SEC-DOCUMENT>