Theatre (in American English usually theater) is a collaborative form of fine art that uses live performers to present the experience of a real or imagined event before a live audience in a specific place. The performers may communicate this experience to the audience through combinations of gesture, speech, song, music or dance. Elements of design and stagecraft are used to enhance the physicality, presence and immediacy of the experience. The specific place of the performance is also named by the word "theatre" as derived from the Ancient Greek θέατρον (théatron, “a place for viewing”) and θεάομαι (theáomai, “to see", "to watch", "to observe”).

Modern Western theatre derives in large measure from ancient Greek drama, from which it borrows technical terminology, classification into genres, and many of its themes, stock characters, and plot elements. Theatre scholar Patrice Pavis defines theatricality, theatrical language, stage writing, and the specificity of theatre as synonymous expressions that differentiate theatre from the other performing arts, literature, and the arts in general.

Theatre today includes performances of plays and musicals. Although it can be defined broadly to include opera and ballet, those art forms are outside the scope of this article.