Ermioni (Greek Ερμιόνη, Ancient Greek Hermione Ἑρμιόνη, Ἑρμιών) is a small town and a former municipality in Argolis, Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Ermionida, of which it is a municipal unit. It is a popular tourist resort. It is on a very small out-cropping of the land facing the island of Hydra. You can reach Ermioni within two hours from Athens by Hydrofoil. The ancient country of Ermionis used to lie in this area. It is linked by a road linking Kranidi and Galatas along with Poros. It is located SE of Argos and Nafplio, about ESE of Lygouri, SW of Troizina, about 10 km E of Kranidi and 17 km NE of Porto Cheli. The island of Dokos lies directly to the southeast.

Much of the area is rocky and sparsely forested. Mountains with a few valleys surround Ermioni. The harbor of Ermioni lies to the south.

The place has been continuously inhabited, at least since the times of Homer. Long before classical times it was settled by Dryopians. During the classic era it was well known for its shipbuilders and also for the production of porphyra, a very important red dye. This dye was used for the colouring of the uniforms of many armies including that of Alexander the Great. Pausanias described the major temples and buildings, various festivities and sport games of the town. During the Turkish Era it was still known for their ship building and its naval abilities, which played a significant role in the Greek revolution of 1821.