Oia or Ia (Greek: Οία, pronounced ) is a small village and former community in the South Aegean on the islands of Thira (Santorini) and Therasia, in the Cyclades, Greece. Since the 2011 local government reform it has been part of the municipality of Santorini, of which it is a municipal unit. It covers the whole island of Therasia and the northwesternmost part of Santorini, which it shares with the municipal unit of Santorini. The main street is named Nikolaou Nomikou. The population was 1,545 inhabitants at the 2011 census, and the land area is 19.449 km2.