Elafonisos (Ελαφόνησος) is a small island off the coast of the Peloponnese. The area of the island is just 19 square kilometres.

Elafonisos is by far the largest inhabited island in the Peloponnese archipelago, and the only one that is a separate municipality. There are also some archaeological discoveries to explore on the island and in the surrounding waters. The main church is Agios Spyridon, which is built on a separate, tiny piece of land which is connected by a bridge to the rest of the island. Elafonisos is a popular holiday destination due to its sandy beaches and turquoise waters.

In antiquity, Elafonisos did not constitute an island but a peninsula with the name Onou Gnathos. It took its current form after a devastating earthquake in the year of 375, which divided Elafonisos from mainland Peloponnese.