Islam is the largest religion of Turkey. More than 99 percent of the population is registered as Muslim, mostly Sunni; however, a 2007 survey found that about 3% of adults define their relation with religion as "having no religious conviction" or "not believing in religious obligations". The Shia Alevi community, a distinct Muslim sect, make up 20 percent of the population. Christianity (Oriental Orthodoxy, Greek Orthodox and Armenian Apostolic) and Judaism are the other religions in practice, but the non-Muslim population declined in the early 2000s.

Turkey is officially a secular state with no official religion since the constitutional amendment in 1924 and later strengthened in the Kemalist Ideology, alongside theAtatürk's reforms and the appliance of laïcité by Mustafa Kemal Atatürk at the end of 1937. To some Turks, Islam is an important part of Turkish life. Its application to join theEU divided existing members, some of which questioned whether a Muslim country could fit in. Turkey accused its EU opponents of favouring a "Christian club".

Beginning in the 1980s, the role of religion in the state has been a divisive issue, as influential factions challenged the complete secularization called for by Kemalism and the observance of Islamic practices experienced a substantial revival. In the early 2000s, Islamic groups challenged the concept of the secular state with increasing vigor after the Erdoğan government had calmed the issue in 2003.