Theatre (Commonwealth English and widespread usage among theatre professionals in the U.S.) or theater (American English) is that branch of the performing arts concerned with acting out stories in front of an audience using combinations of speech, gesture, music, dance, sound and spectacle — indeed any one or more elements of the other performing arts.

In addition to the standard narrative dialogue style, theatre takes such forms as opera, ballet, mime, kabuki, classical Indian dance, Chinese opera, mummers' plays, and pantomime.

The word 'theatre' is also used for the building in which works and plays are performed.

There is an enormous variety of philosophies, artistic processes, and theatrical approaches to creating plays and drama. Some are connected to political or spiritual ideologies, and some are based on purely "artistic" concerns. Some processes focus on a story, some on theatre as an event, some on theatre as a catalyst for social change. According to Aristotle's seminal theatrical critique Poetics, there are six elements necessary for theatre. They are Plot, Character, Idea, Language, Song, and Spectacle.