Improvisational comedy (also called improv) is comedy that is performed with a minimum of preparation concerning subject matter and structure. The performers make up their material spontaneously in their performances, typically following a general theme and format, often in response to audience suggestions. Improvisational comedy is a form of improvisational theater.

Improvised performance is as old as performance itself. Many silent filmmakers like Charles Chaplin and Buster Keaton used this approach in the making of their films in which they worked up their gags as their films were produced and changed the film plot accordngly to fit. In modern times, stand-up comedians like Robin Williams often use improvisation onstage.

A more structured form of improv is used by troupes like Second City, ImprovOlympic, and The Groundlings. These groups develop scenes using a specific set of rules, usually keyed by audience suggestions. Different rules may be used for different scenes, with the objective to create spontaneous comedy by forcing the performers to react to the current situation rather than rely on a script. Improv comedy forms the basis of the television show Whose Line is it Anyway. Improv comedy techniques have also been used in more recent films, notably the mockumentary films of director Christopher Guest.

See also: Theatresports