Islam in Greece is represented by two distinct communities; Muslims that have lived in Greece since the times of the Ottoman Empire (primarily in East Macedonia and Thrace) and Muslim immigrants that began arriving in the last quarter of the 20th century, mainly in Athens and Thessaloniki.
The Muslim population in Greece is not homogeneous, since it consists of different ethnic, linguistic and social backgrounds which often overlap. The Muslim faith is the creed of several ethnic groups living in the present territory of Greece, namely the Pomaks, ethnic Turks, certain Romani groups, and Greek Muslims particularly of Crete, Epirus, and western Greek Macedonia who converted mainly in the 17th and 18th centuries. The country's Muslim population decreased significantly as a result of the 1923 population exchange agreement between Greece and the new Turkish Republic, which also uprooted approximately 1.5 million Greeks from Asia Minor. Many of the Muslims of Northern Greece were actually ethnic Greek Muslims from Epirus and Greek Macedonia, whereas the Muslims of Pomak and ethnic Turkish origin (the Western Thrace Turks) from Western Thrace were exempt from the terms of the population exchange. Successive Greek governments and officials consider the Turkish-speaking Muslims of Western Thrace as part of the Greek Muslims minority and not as a separate Turkish minority. This policy is aimed to give the impression that the Muslims of the region are the descendants of Ottoman-era ethnic Greek converts to Islam like the Vallahades of pre-1923 Greek Macedonia and so thereby avoid a possible future situation in which Western Thrace is ceded to Turkey on the basis of the ethnic origin of its Muslim inhabitants.