The Gulf of Corinth is the body of water separating Peloponnese from western mainland Greece. It is bounded in the east by the Isthmus of Corinth which includes the shipping route of the Corinth Canal, and in the west by the strait of Rio-Antirio, crossed by the Rio-Antirio bridge. It is almost surrounded by the prefectures of Aitoloacarnania, Phokida in the north, Viotia in the northeast, Attica in the east, Corinthia in the southeast and south and Achaea in the southwest.

The Gulf was created by the expansion of a tectonic rift, and still expands by about 30 mm per year. The surrounding faults have important seismic activity.