The port town Ermioni is situated in the southeastern part of Argolis, on the coast of the Aegean Sea. It faces the islands of Hydra and Dokos. The municipal unit Ermioni also contains the communities Iliokastro (7 km north of Ermioni) and Thermisia (7 km east of Ermioni). It is 10 km east of Kranidi, 22 km southwest of Galatas and 44 km southeast of Nafplio. Ermioni is connected to Piraeus by ferry.
The place has been continuously inhabited, at least since the times of Homer. Long before classical times ancient Hermione 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. It controlled a wider region named Hermionis. Pausanias described the major temples and buildings, various festivities and sport games of the town. During the Turkish Era it was still known for ship building and its naval abilities, which played a significant role in the Greek revolution of 1821.