Kythira (, ; Greek: Κύθηρα, [ˈciθira], also transliterated as Cythera, Kythera and Kithira) is an island in Greece lying opposite the south-eastern tip of the Peloponnese peninsula. It is traditionally listed as one of the seven main Ionian Islands, although it is distant from the main group. Administratively, it belongs to the Islands regional unit, which is part of the Attica region, despite its distance from the Saronic Islands, around which the rest of Attica is centered. As a municipality, it includes the island of Antikythera to the south.

The island is strategically located between the Greek mainland and Crete, and from ancient times until the mid 19th century was a crossroads of merchants, sailors, and conquerors. As such, it has had a long and varied history and has been influenced by many civilizations and cultures. This is reflected in its architecture (a blend of traditional, Aegean and Venetian elements), as well as the traditions and customs, influenced by centuries of coexistence of the Greek, and Venetian cultures.