Improvisational theatre (also known as improv or impro) is a form of theatre in which the actors use improvisational acting techniques to perform spontaneously. Actors typically use audience suggestions to guide the performance as they create dialogue, setting, and plot extemporaneously. Improvisational theatre performances tend to be comedic, although some forms, including Playback Theatre and Theatre of the Oppressed, are not necessarily intended to be comedic.
Many improvisational actors also work as scripted actors, and "improv" techniques are often taught in standard acting classes. The basic skills of listening, clarity, confidence, and performing instinctively and spontaneously are considered important skills for actors to develop.
Modern improvisational comedy, as it is practiced in the West, falls generally into two categories: shortform and longform.
Shortform improv consists of short scenes usually constructed from a predetermined game, structure, or idea and driven by an audience suggestion. Many shortform games were first created by Viola Spolin. The shortform improv comedy television series Whose Line Is It Anyway? has familiarized American and British viewers with shortform.
Longform improv performers create shows in which scenes are often interrelated by story, characters, or themes. Longform shows may take the form of an existing type of theater, for example a full-length play or Broadway-style musical such as Spontaneous Broadway. Longform improvisation is especially performed in Chicago and New York City. Perhaps the best-known, and considered the first, longform structure is the Harold, developed by ImprovOlympic cofounder Del Close.