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X UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , DC 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission file number 0-24531 Delaware ( State or other jurisdiction of incorporation or organization ) to CoStar Group ™ CoStar Group , Inc. ( Exact name of registrant as specified in its charter ) 1331 L Street , NW Washington , DC 20005 ( Address of principal executive offices ) ( zip code ) ( I.R.S. Employer Identification No. ) ( 202 ) 346-6500 ( Registrant's telephone number , including area code ) Trading Symbol CSGP 52-2091509 Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock ( $ 0.01 par value ) Securities registered pursuant to section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Name of each exchange on which registered Nasdaq Global Select Market Yes x No o Yes o No x Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes x No o Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes x No O