The Island depends on tourism, and Athenians account for a sizable segment of its visitors. High-speed hydrofoils and catamarans from Piraeus, some 37 nautical miles (69 km) away, serve Hydra, stopping first at Poros before going on to Spetses. There is a passenger ferry service providing an alternative to Hydrofoils that runs from Hydra Harbor to Metochi on the Peloponnese coast. Many Athenians drive to Metochi, leave their car in the secure car park, and take the 20-minute passenger ferry across to Hydra.
Rubbish trucks are the only motor vehicles on the island, as cars and motorcycles are not allowed by law. Horses, mules and donkeys, and water taxis provide public transportation. The inhabited area, however, is so compact that most people walk everywhere.
Hydra benefits from numerous bays and natural harbors, and has a strong maritime culture. The island is a popular yachting destination and is the home of the Kamini Yacht Club, an international yacht club based in the port of Kamini.
In 2007, a National Geographic Traveler panel of 522 experts rated Hydra the highest of any Greek island (11th out of 111 islands worldwide) as a unique destination preserving its "integrity of place."
There is evidence of farmers and herders from the second half of the third millennium BCE on the small, flat areas that are not visible from the sea. Obsidian from Milos has also been found. During the Helladic period, Hydra probably served as a maritime base for the kingdoms on the Greek peninsula. Fragments of vases, tools, and the head of an idol have been found on Mount Chorissa.
The large-scale Dorian invasion of Greece around the 12th century BCE appears to have depopulated the island.
Hydra was repeopled by farmers and herders, perhaps sailing from the mainland port of Ermioni, in the 8th century BCE. Herodotus reports that toward the 6th century BCE, the island belonged to Ermioni, which sold it to Samos. Samos, in turn, ceded it to Troizina.
For much of its existence, Hydra stayed on the margins of history. The population was very small in ancient times and, except for the brief mentions in Herodotus and Pausanias, left little or no record in the history of those times.
It is clear that Hydra was populated during the Byzantine Era, as vases and coins have been discovered in the area of Episkopi. However, it appears that the island again lost its population during the Latin Empire of Constantinople as its inhabitants fled the pirate depredations. On other islands, inhabitants moved inland, something that was essentially impossible on Hydra.
From 1204 to 1566, it belonged to Venice. From 1566 to 1821 (nominally 1829), it was part of the Ottoman Empire.
In the 16th century, the island began to be settled by refugees from the warfare between the Ottomans and Venetians. The Arvanites' presence was evident until the mid-20th century, when, according to T. Jochalas, the majority of the island's population was composed of Arvanites. The island is known in Arvanitika as Nίδρα.