It is the largest island of a small circular archipelago, which bears the same name and is the remnant of a caldera.

It forms the southernmost member of the Cyclades group of islands, with an area of approximately 73 km2 and a 2011 census population of 15,550.

The municipality of Santorini includes the inhabited islands of Santorini and Therasia, as well as the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi and Christiana. The total land area is 90.623 km2. Santorini is part of the Thira regional unit.