Selçuk is the central town of Selçuk district, Izmir Province in Turkey, 2 kilometres (1 mile) northeast of the ancient city of Ephesus.

Its original Greek name, Agios Theologos, referred to John the Theologian, because emperor Justinian had erected there a basilica in honour of the saint. Ayasoluk is a corrupted form of the original name. In the 14th century, it was the capital of the Beylik of Aydin, and visited by Ibn Battuta. He noted, "The congregational mosque in this city is one of the most magnificent mosques in the world and unequaled in beauty." Under the Ottoman Empire, it was known as Ayasoluk. In 1914, it was renamed Selçuk after the Seljuk Turks who first led incursions into the region in the 12th century.

It was a township in Kusadasi district till 1957, when it became a district itself. Its neighbours are Torbali from north, Tire from northeast, Germencik from east, Kusadasi from south, Aegean Sea from west and Menderes (formerly Cumaovasi) from northwest.

Selçuk is one of the most visited tourist destinations within Turkey, known for its closeness to the ancient city of Ephesus, House of the Virgin Mary and Seljuk works of art. The 6th century Basilica of St. John the Apostle, which, some claim, is built on the site of the Apostle's tomb, is also inside the town. Procopius said that the basilica was a most sacred and honoured place in Ephesus. It was severely damaged in the invasion of Selçuk Turks in 1090. The place was excavated in 1927, and Pope Paul VI paid it a visit and prayed there.

In 1921, after the capture of the village by the Greek forces, the village had a total population of 600, ethnographically consisting of 580 Greeks, 10 Turks and 10 Armenians.

The old quarter of Selçuk retains much traditional Turkish culture. Ayasuluk Hill dominates the surrounding area, with several historical buildings on its slopes, including the Isa Bey Mosque built by the Aydinids in 1375, and the Grand Fortress. The hill itself is part of Ephesus UNESCO World Heritage Site.

Ephesus Beach (Turkish: Pamucak) is one of the longest beaches (12 km) in Turkey and hosts five large hotels.