Oia or Ia (Greek: Οία, romanized: Oía, pronounced [ˈia][2]) is a small village and former community in the South Aegean on the islands of Thira (Santorini) and Therasia, in the Cyclades, Greece.

Its economic prosperity was based on its merchant fleet, which plied trade in the Eastern Mediterranean, especially from Alexandria to Russia.

[8] Under the da Corogna family, Agios Nikolaos Kastell (Καστέλι του Αγίου Νικολάου), also called Apanomeria (Απανωμερία), was one of five local citadels.

The economy of the town declined in the early 20th century on account of wars, economic depression and over extraction of fish resources.

[12] It extends for almost two kilometres (1+1⁄4 mi) along the northern edge of the caldera that forms the island of Santorini, at a height of between 70 and 100 metres (230 and 330 ft) above sea level.

The small fishing village of Ormos Armeni (Όρμος Αρμένης) lies below Oia to the south and is reached via steps.

There is a ferry connection to Therasia from the harbour village of Ormos Ammoudi (Όρμος Αμμουδιού; also spelled Amoudi)[12] to the west.

The harbour of Ammoudi on the western side of the town is reached by steep stairs north of Fort Londsa; there are a few tavernas and a pebble beach.

[6][2] The village is located on top of a hill, at about 150 m (500 ft) elevation, and known as the "Eagles nest" from where Palia and Nea Kameni volcanoes are seen and also the island of Therasia.

Under the Kapodistrias plan of 1997, it was combined with Therasia to form the rural community of Oia, Kinotita Ias (Κοινότητα Οίας).

Under the 2010 Kallikratis plan for administrative reform which took effect on 1 January 2011, this was folded into the newly created municipality of Santorini, Dimos Thiras (Δήμος Θήρας), as the district of Oia (Δημοτική Κοινότητα Οιας).

[14] In 1976 the town was included in the programme for preservation and development of traditional settlements of the Greek National Tourism Organisation under Aris Konstantinidis.

Many of the yposkafa spitia (υπόσκαφα σπίτια), simple seamen's houses on the edge of the caldera, became guest-houses, hotels and restaurants.

The other explanation given is that during the Ottoman rule of Greece, which lasted for over 400 years, Greeks were not allowed to fly their white flag.

[14] Other infrastructure and cultural facilities available in the town are a cultural centre, a bank, ATMS cash services, an internet café, a bus station, a post office, a health clinic and pharmacy, apart from the cafes, bars, restaurants and taverns on the coastal path.

At this time the town is crowded with people to watch the spectacle, when the white houses and the caldera catch all the colours of the setting sun for a few seconds.

[6] Another 19th-century mansion in Oia, a block away from the cliff-top, has been restored and converted into the municipal museum of the maritime history of Thira.

It displays rare figureheads, ancient nautical charts with English labels, seamen's chests, old maritime equipment such as mastheads, drawings and patterns, models of old and new Thiran ships and historic photographs and has a library containing many letters and documents.

[22] Oia was also featured in the opening sequences of the film Lara Croft Tomb Raider: The Cradle of Life, starring Angelina Jolie.