Sybaris (Ancient Greek: Σύβαρις; Italian: Sibari) was an important city of Magna Graecia. It was situated in modern Calabria, in southern Italy, between two rivers, the Crathis (Crati) and the Sybaris (Coscile).

The city was founded in 720 BC by Achaean and Troezenian settlers. Sybaris amassed great wealth thanks to its fertile land and busy port. Its inhabitants became famous among the Greeks for their hedonism, feasts, and excesses, to the extent that "sybarite" and "sybaritic" have become bywords for opulence, luxury, and outrageous pleasure-seeking.

In 510/509 BC the city was subjugated by its neighbor Kroton and its population driven out. Sybaris became a dependent ally of Kroton, but Kroton again besieged the city in 476/475 BC, probably resulting in another victory for Kroton. Two attempts to reoccupy the city failed around 452/451 BC and 446/445 BC when the remaining Sybarites were again expelled by the Krotoniates. After a call for help the Sybarites reoccupied their city later in 446/445 BC with the assistance of new settlers from Athens and other cities in the Peloponnese. This coexistence did not last long: the Sybarites got into a conflict with the new colonists and were ousted for the last time in the summer of 445 BC. In sum, the city saw a total of five periods of occupation separated by expulsion. The new settlers then proceeded to found the city of Thurii in 444/443 BC, a new colony which was built partially on top of the site of Sybaris. The surviving Sybarites founded Sybaris on the Traeis.

The ruins of Sybaris and Thurii became forgotten as they were buried by sediment from the Crati river. The ruins were rediscovered and excavated in the 1960s by Donald Freeman Brown. Today they can be found southeast of Sibari, a frazione in the comune of Cassano allo Ionio in the Province of Cosenza, Calabria region, Italy.