A black box theater (or experimental theater) consists of a simple, somewhat unadorned performance space, usually a large square room with black walls and a flat floor. It is a relatively recent innovation in theatre. Not to be confused with black light theater, which is also known as black theater.
Black box theaters became popular and widespread particularly in the 1960s and 1970s. Since almost any large room, including abandoned cafés, stores and warehouses can be transformed into a black box, cost can be low, which appeals to nonprofit and low-income artists. The black box is also considered by many to be a place where more "pure" theatre can be explored, with the most human and least technical elements being in focus.
The concept of a building designed for flexible staging techniques can be attributed to Swiss designer Adolphe Appia, circa 1921, and instigated a half century of innovations in the relationship between audience and performers. Antonin Artaud also had ideas of a stage of this kind. The first flexible stage in America (not a proper Black Box due to the domestic decor) was located in the home living room of actor/manager Gilmor Brown in Pasadena, CA. This venue, and two subsequent permutations, were known as the Playbox Theatre, and functioned as an experimental space for Brown's larger venue, the Pasadena Playhouse.
Such spaces are easily built and maintained, and are usually home to plays or other performances with very basic technical arrangements, such as limited Set construction. Common floor plans include thrust stage, modified thrust stage, and theater in the round.
Colleges and other theater training programs employ the black box theater because the space is versatile and easy to change. Many theater training programs will have both a large proscenium theater, as well as a black box theater. Not only does this allow two productions to be mounted simultaneously, but they can also have a large extravagant production in the main stage while having a small experimental show in the black box.