The earliest signs of inhabitation on the island suggest it the influence of settlers from the shores of Asia Minor. The island later witnessed the destruction of Minoan civilization (2000-1500 B.C.) on Santorini from a volcanic eruption. The Dorians and Ionians arrived on the island sometime around 1100 B.C. and gave it its present-day name. Ios joined the Athenian League (or Confederacy). In the early 13th century, it came under Venetian rule; in 1397, Marcus Crispus, the island's governor, fortified Chora with defensive walls (Kastro), whose ruins are visible today.

In 1537, the island fell to the Turks, who dubbed it "Little Malta" because the natural shelter offered by its harbor.  The island suffered under its Turkish rules, who imposed heavy taxes and other punishments. During this time, the island also suffered from pirate raids.  

The island claims among its native sons Spyridon Valetas (1718-1843), a member of the revolutionary Filike Etaireia who distinguished himself in the Greek war of independence. Valetas later became the first Minister of Education of the Modern Greek State.

Ios is known as the home of Clemene, mother of the greatest epic poet of all time, Homer, who wrote The Odyssey and The Iliad in the eighth century B.C. Homer's grave is at Plakotos and in local lore he died on the island while trying to solve a riddle he was told by fishermen at Plakotos.

Ios is an island of the Cyclades and is located between Naxos, Sikinos and Santorini. Its area is 108 km2, its maximum length is 17 km and its width 7.5 km. Ios has 87 kilometers of coastline which is estimated to be sandy beaches around 30 km. The distance of Ios from the port of Piraeus is 110 nm, from Heraklion in Crete it is 72 nm, while from Syros it is 55 nm.
The population of Ios at the 2001 census was 1.838 inhabitants, of whom 1.632 lived in Ios Town, the capital of the island.
It is a mountainous island, with highest peaks those of Pyrgos (732 m) and Profitis Ilias (500 m), although there are available cultivating valleys as well.
The climate of the island is cool so that, even in high temperatures (June-August 28oC), the meltemia will refresh locals and visitors. The average temperature in the hot summer months ranges from 27οC-29οC while in other seasons 12οC-18οC.
Until recently, the economy was based mainly on agriculture (cereals, olives, wine) and cattle-breeding.
Nowadays the residents are involved with the tourism. A traditional type of land cultivation, dating back to the 6th century BC, is the system of terraces, “pezoules”, created with the help of retaining walls made of dry stone and they allow the cultivation in lands with big gradient.