Nominally, 99% of the population is Muslim . Most belong to the Sunni branch of Islam. About 15-20% of the population are Alevi Muslims. There is also a small but significant Twelver Shi'a minority, mainly of Azeri descent. The remaining 1% of the population are of other religions, mostly Christian ( Greek Orthodox , Armenian Apostolic (Gregorian), Syriac Orthodox , Roman Catholics and Protestants ), Jewish , Bahá'ís , Yezidis .

Unlike other Muslim -majority countries, there is a strong tradition of separation of church and state in Turkey. Even though the state does not have any/or promote any religion, it actively monitors the area between the religions. The constitutional rule that prohibits discrimination on religious grounds is taken very seriously. The Turkish constitution recognises freedom of religion for individuals , and the religious communities are placed under the protection of state, but the constitution explicitly states that they cannot become involved in the political process, by forming a religious party for example. No party can claim that it represents a form of religious belief. However, the religious sensibilities are generally represented through conservative parties.

The mainstream Hanafite school of Sunni Islam is largely organised by the state, through Diyanet İşleri Başkanlığı (Department of Religious Affairs). The Diyanet is the main Islamic framework established after abolition of the Ulama and Seyh-ul-Islam of the old régime. As a consequence, they control all mosques and Muslim clerics. Imams are trained in Imam Hatip schools and at theology departments at universities. The department supports Sunni Islam and has commissions authorised to give Fatwa judgements on Islamic issues. The department is criticized by some Alevi Muslims for not supporting their beliefs.

The Orthodox Patriarch ( Patrik ) governs the Greek-Orthodox Church in Turkey and acts as the spiritual leader of all Orthodox churches throughout the world, the Armenian Patrik the Armenian Church, while the Jewish community is lead by the Hahambasi , Turkey's Chief Rabbi , all based in Istanbul. The Jewish population in Turkey is one of the largest and most prominent outside of Israel .

Source: Wikipedia