CoStar Group, Inc. is an American commercial real estate information and marketing provider with headquarters in Washington, DC. The company has approximately 3,500 employees.

CoStar Group, Inc. (CoStar) was founded in 1987 by Andrew Florance in Washington, DC. CoStar is a provider of information, analytics and marketing services to the commercial real estate industry in the United States, Canada, the United Kingdom, France, Germany and Spain. The company’s suite of online service offerings includes information about space available for lease, comparable sales information, tenant information, information about properties for sale, Internet marketing services, analytical capabilities, information for clients' Websites, information about industry professionals and their business relationships, data integration and industry news. Its service offerings span all commercial property types, including office, industrial, retail, land, mixed-use, hospitality and multifamily. CoStar Group went public in 1998 and is traded on the NASDAQ under the symbol CSGP. In April 2012, CoStar Group completed the acquisition of LoopNet, Inc for $860 million. In April 2014, CoStar Group completed the acquisition of Apartments.com for $585 million. In April 2015, CoStar Group announced an agreement to acquire Apartment Finder. In October 2016, CoStar Group announced that Richmond, VA will be the new research headquarters.

Jeff Goldblum introduced Apartments.com in a set of ads in 2015 portraying fictional character Brad Bellflower, a tech futurist. Bob Odenkirk directed Goldblum in the 2016 ad campaign, which continued with the Bellflower character.