Whose Line is it Anyway? (shortened to Whose Line? or WLIIA) is a short-form improvisational comedy television panel show created by Dan Patterson and Mark Leveson, presented by Clive Anderson, and produced for Channel 4 between 23 September 1988 and 4 February 1999. The programme features a panel of four performers, (six in the Christmas special), conducting a series of short-form improvisation games, creating comedic scenes per predetermined situations made by the host or from suggestions by the audience. Such games include creating sound effects, performing a scene to different television and film styles, using props, and making up a song on the spot. The programme originally began as a short-lived BBC radio programme, before the concept was adapted for television.

During its history, the programme featured a variety of noted comedians from Britain, America and Canada. Frequent performers during the show's run included John Sessions, Stephen Fry, Archie Hahn, Josie Lawrence, Paul Merton, Rory Bremner, Tony Slattery, Mike McShane, Greg Proops, Ryan Stiles, Sandi Toksvig, Jim Sweeney, Colin Mochrie, Steve Steen, Stephen Frost, Chip Esten, Brad Sherwood, Caroline Quentin and Wayne Brady. The programme was mainly recorded in Britain, though several episodes of series 3 and 4 were made in New York, while the tenth and final series was shot entirely in California.

The success of Whose Line? spawned several domestic and international adaptations. An American version aired on ABC between 1998 and 2007 and was revived on The CW in 2013, and is broadcast in multiple countries. Whose Line Is It Anyway? Australia debuted on The Comedy Channel in 2016. Two similarly themed British comedy programmes, Mock the Week (2005–2022) and Fast and Loose (2011), were created by Patterson.