Improvisation theatre, improv theatre, or simply improv, is a form of theatre that is improvised: none of the presented scenes are previously rehearsed. This is the main difference from classical theatre.
Often the actors receive a suggestion from the audience, or even repeatedly receive input during a scene. These suggestions serve as a leitmotif or impulse generator for the spontaneously emerging scenes. Improv theatre is frequently accompanied by music. The music is also improvised and intimately interwoven with the stage performance.
The stories arise from the actors’ mutual inspiration. Preplanned acting gives way to the pure, spontaneous interplay of action and reaction between the actors.
There is a distinction between short and long forms in improvisational theatre. The short forms consist of scenes that only take a few minutes, stand on their own, or that are connected by an overarching thematic motif, but not connected to each other.
There are many concepts for these short forms. In "theatre sports" teams of actors encounter each other and vie for the favour of the audience. There is also the Maestro improv format, which determines the best actor of the evening. There are theatre sports teams all over the world, and theatre makers have developed similar theatrical concepts, and there are crossovers. The term “theatersport” is a non-registered trademark.
The short forms dominate the "games" most of the time, which often leads to a comical interpretation of improv theatre. While this is often the case, is does not have to be. With the improvised long forms, however, the serious scenes tend to dominate, but comic elements may also be used.
A format called "Harold" takes up a topic suggestion from the audience and the actors create a kind of closely interwoven scenic collage out of various aspects of this topic, with partially-developed characters and psychological depth.
Another long form is the Improv murder mystery, using various formats, which differ in particular due to audience participation.
There is also biography theatre. An invited guest talks about his life. This story is improvised at the same time. With Improv theatre this tends more to be entertaining, and in playback theatre to be more psychologizing.
Good and interesting Improv stories emerge if the actors bear in mind certain principles. These include the often touted "joy in failure", playing in the here and now, and acting using one’s own state.
Since this kind of acting also enables a special type of open communication, many actors see their passion for improv theatre as more than just a kind of recreation, but much more as the acting out of an inner attitude to life. This close association with one’s own philosophy of life differs perhaps from classical theatre.