Gytheio or Gythio, also the ancient Gythium or Gytheion, is a town on the eastern shore of the Mani Peninsula, and a former municipality in Laconia, Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality East Mani, of which it is a municipal unit. The municipal unit has an area of 197.313 km2.

The Mani Peninsula, also long known by its medieval name Maina or Maïna, is a geographical and cultural region in the Peloponnese of Southern Greece and home to the Maniots, who claim descent from the ancient Spartans. The capital city of Mani is Areopoli. Mani is the central of three peninsulas which extend southwards from the Peloponnese. To the east is the Laconian Gulf, to the west the Messenian Gulf. The Mani peninsula forms a continuation of the Taygetos mountain range, the western spine of the Peloponnese.