Ephesus (Ancient Greek Ἔφεσος, Turkish Efes) was an ancient Greek city on the west coast of Anatolia, near present-day Selçuk, Izmir Province, Turkey. It was one of the twelve cities of the Ionian League during the Classical Greek era. In the Roman period, it was for many years the second largest city of the Roman Empire; ranking behind Rome, the empire's capital.Ephesus had a population of more than 250,000 in the 1st century BC, which also made it the second largest city in the world.

The city was famed for the Temple of Artemis (completed around 550 BCE), one of the Seven Wonders of the Ancient World. The temple was destroyed in 401 CE by a mob led by St. John Chrysostom. Emperor Constantine I rebuilt much of the city and erected new public baths. The town was again partially destroyed by an earthquake in 614. The city's importance as a commercial center declined as the harbor was slowly silted up by the Cayster River (Küçük Menderes).

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. It is also the site of a large gladiators' graveyard Today's archaeological site lies 3 kilometers southwest of the town of Selçuk, in the Selçuk district of İzmir Province, Turkey. The ruins of Ephesus are a favorite international and local tourist attraction..

Ephesus was an important center for Early Christianity from the AD 50s. From AD 52-54, Paul lived in Ephesus, working with the congregation and apparently organizing missionary activity into the hinterlands. He became embroiled in a dispute with artisans, whose livelihood depended on selling the statuettes of Artemis in the Temple of Artemis (Acts 19:23–41). He wrote between 53 and 57 AD the letter 1 Corinthians from Ephesus (possibly from the "Paul tower" close to the harbour, where he was imprisoned for a short time). Later Paul wrote the Epistle to Ephesians while he was in prison in Rome (around 62 AD)

The house of the Virgin Mary, about 7 km (4 mi) from Selçuk, is believed to have been the last home of Mary, mother of Jesus. It is a popular place of pilgrimage which has been visited by three recent popes.