Welcome to The Improv Page, a clearinghouse for information about improvisational theatre.
Improvisation is a form of theatre in which no script is used. Instead, the actors create the dialog and action themselves, as they perform. The most popular style today is "spot" improv, in which performers get suggestions from their audience and use them to create short, entertaining scenes.
No matter where or how it's performed, the essential ingredient in any improvisational performance is that the audience and the actors are working together to create theatre.