Ephesus (Turkish: Efes) was an ancient Greek city, and later a major Roman city, on the coast of Ionia, near present-day Selçuk, Izmir Province. It was one of the twelve cities of the Ionian League during the Classical Greek era. In the Roman period, Ephesus had a population of more than 250,000 in the 1st century BC, which served to make it one of the largest cities in the Mediterranean world.

The city was famed for the Temple of Artemis (completed around 550 BC), one of the Seven Wonders of the Ancient World. Emperor Constantine I rebuilt much of the city and erected new public baths. In 268 AD, the Temple was destroyed or damaged in a raid by the Goths. It may have been rebuilt or repaired but this is uncertain, as its later history is not clear. Following the Edict of Thessalonica from emperor Theodosius I, what remained of the temple was destroyed in 401 AD by a mob led by St. John Chrysostom. The town was partially destroyed by an earthquake in 614 AD. The city's importance as a commercial center declined as the harbor was slowly silted up by the Cayster River.

Ephesus was one of the seven churches of Asia that are cited in the Book of Revelation. The Gospel of John may have been written here. The city was the site of several 5th-century Christian Councils. It is also the site of a large gladiators' graveyard.

The ruins of Ephesus are a favorite international and local tourist attraction, partly owing to their easy access from Izmir's Airport.