Turkey is a secular state with no official state religion; the Turkish Constitution provides for freedom of religion and conscience. Islam is the dominant religion of Turkey; it exceeds 99% if secular people of Muslim background are included, with the most popular sect being the Hanafite school of Sunni Islam. The highest Islamic religious authority is the Presidency of Religious Affairs (Turkish: Diyanet Isleri Baskanligi), it interprets the Hanafi school of law, and is responsible for regulating the operation of the country’s 80,000 registered mosques and employing local and provincial imams. Academics suggest the Alevi population may be from 15 to 20 million. According to Aksiyon magazine, the number of Shiite Twelvers (excluding Alevis) is 3 million (4.2%). There are also some Sufi practitioners. Roughly 2% are non-denominational Muslims.

The percentage of non-Muslims in Turkey had fallen from 19.1% in 1914 to 2.5% in 1927. Currently, there are about 120,000 people of different Christian denominations, representing less than 0.2% of Turkey’s population, including an estimated 80,000 Oriental Orthodox,35,000 Roman Catholics, 5,000 Greek Orthodox and smaller numbers of Protestants. Today there are 236 churches open for worship in Turkey. The Eastern Orthodox Church has been headquartered in Istanbul since the 4th century.

Furthermore, there are about 26,000 people who are Jewish, the vast majority of whom are Sephardi. The Bahá’í Faith in Turkey has roots in Bahá’u’lláh’s, the founder of the Bahá’í Faith, being exiled to Constantinople, current-day Istanbul, by the Ottoman authorities. Bahá’ís cannot register with the government officially, but there are probably 10 to 20 thousand Bahá’ís, and around a hundred Bahá’í Local Spiritual Assemblies in Turkey.

The role of religion has been a controversial debate over the years since the formation of Islamist parties. For many decades, the wearing of the hijab was banned in schools and government buildings, because it was viewed as a symbol of political Islam. However, the ban was lifted for the universities in 2011 and for the government buildings in 2013. In a KONDA survey, 69.4% of the respondents reported that they or their wives cover their heads (1.3% reporting chador), although this rate decreases in several demographics: 53% in ages 18–28, 27.5% in university graduates, 16.1% in masters-or-higher-degree holders. There are also regional variations, with 30% of women in Istanbul reporting covering their hair.

According to the KONDA Research and Consultancy survey carried out throughout Turkey on 2007: 9.7% defined themselves as “a fully devout person fulfilling all religious obligations” (fully devout); 52.8% defined themselves as “a religious person who strives to fulfill religious obligations” (religious); 34.3% defined themselves as “a believer who does not fulfill religious obligations” (believer); 2.3% defined themselves as “someone who does not believe in religious obligations” (non-believer/agnostic); and 0.9% defined themselves as “someone with no religious conviction” (atheist)