The Peloponnese or Peloponnesus is a large peninsula and region in southern Greece, forming the part of the country south of the Gulf of Corinth. The peninsula is divided among three distinct peripheries of modern Greece: most of the Peloponnese and parts of the West Greece and Attica peripheries.

The Peloponnese covers an area of some 21,549 km² (8,320 square miles) and constitutes the southernmost part of mainland Greece. While technically it may be considered an island since the construction of the Corinth Canal in 1893 - like other peninsulas that have been separated from their mainland by man-made bodies of waters - it is rarely, if ever, referred to as an "island". It has two land connections with the rest of Greece, a natural one at the Isthmus of Corinth and an artificial one in the shape of the Rio-Antirio Bridge (completed 2004).