An amphitheatre (or amphitheater) is an open-air venue used for entertainment and performances. The term derives from the ancient Greek ἀμφιθέατρον (amphitheatron), from ἀμφί (amphi), meaning "on both sides" or "around" and θέατρον (théātron), meaning "place for viewing".

Ancient Greek theatres were built to a semicircular plan, with tiered seating above a performance area. Ancient Roman amphitheatres were oval or circular in plan, with seating tiers that surrounded the central performance area, like a modern open-air stadium. Modern usage for "amphitheater" can embrace theatre-style stages with the audience only on one side, theatres in the round, and stadiums. Natural formations shaped like man-made theatres or amphitheatres are sometimes known as natural amphitheatres.

Ancient Roman amphitheatres were major public venues, circular or oval in shape, and used for events such as gladiator combats, chariot races, venationes (animal slayings) and executions. About 230 Roman amphitheatres have been found across the area of the Roman Empire. Their typical shape, functions and name distinguish them from Roman theatres, which are usually semicircular in shape; from the circuses (akin to hippodromes) whose much longer circuits were designed mainly for horse or chariot racing events; and from the smaller stadia, which were primarily designed for athletics and footraces.