CSI: Crime Scene Investigation is an American crime drama television series that trails the investigations of a team of Las Vegas forensic scientists as they unveil the circumstances behind mysterious and unusual deaths and other crimes. The show was created by Anthony E. Zuiker and is filmed primarily at Universal Studios in Universal City, California. The pilot episode was first broadcast on October 6, 2000, and eight seasons have been aired. CSI currently airs on Thursdays, at 9:00 p.m. on CBS. In Canada, the show airs on CTV at 8:00 p.m.

CSI is produced by Jerry Bruckheimer Television and CBS Productions, which became CBS Paramount Television in the fall of 2006. Formerly a co-production with the now-defunct Alliance Atlantis Communications, that company's interest in the series is now owned by investment firm GS Capital Partners, an affiliate of Goldman Sachs. CBS Paramount acquired AAC's international distribution rights to the program.

The show has been heavily criticized—almost since its debut—by police and district attorneys, who feel CSI portrays an inaccurate image of how police solve crimes, and by the Parents Television Council, who note the level and gratuitousness of graphic violence, images and sexual content seen on the show. Nevertheless, CSI became the most-watched show on American television by 2002. The success of the show encouraged CBS to produce a franchise, starting in May 2002 with the spin-off CSI: Miami and then again in 2004 with CSI: NY .

The show is now in syndication and reruns are currently broadcast in the US on the Spike and TV Land cable networks.

CBS renewed the show for a ninth season, which began airing on October 9, 2008. With the departures of William Petersen and Gary Dourdan, the ninth season stars new characters played by Lauren Lee Smith and Laurence Fishburne. Lady Heather returned in episode 905 and The Miniature Killer returned in episode 907.

As of the fall of 2008, CSI commands an average cost of $262,200 for a 30-second commercial, according to an Advertising Age survey of media-buying firms.