Islam is the religion with the largest community of followers in the country, where most of the population is nominally Muslim, of whom over 75% belong to the Sunni branch of Islam. Over 20% of the Muslim population is Shia Alevi. There is also a small Bektashi community belonging to a Sufi order of Islam that is indigenous to Turkey, but also has numerous followers in the Balkan peninsula. Islam arrived in the region that comprises present-day Turkey, particularly the eastern provinces of the country, as early as the 7th century AD. The mainstream Hanafi school of Sunni Islam is largely organized by the state, through the Religious Affairs Directorate, which was established in 1924 following the abolition of the Caliphate and controls all mosques and Muslim clerics, and is officially the highest religious authority in the country.

As of today, there are thousands of historical mosques throughout the country which are still active. Notable mosques built in the Seljuk and Ottoman periods include the Sultan Ahmed Mosque and Süleymaniye Mosque in Istanbul, the Selimiye Mosque in Edirne, the Yeşil Mosque in Bursa, the Alaeddin Mosqueand Mevlana Mosque in Konya, and the Great Mosque in Divriği, among many others. Large mosques built in the Republic of Turkey period include the Kocatepe Mosque in Ankara and the Sabancı Mosque in Adana.