Islam is the largest religion in Turkey. More than 99 percent of the population is Muslim, mostly Sunni. 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 a secular state with no official religion since the constitutional amendment in 1924. To some Turks, Islam is an important part of Turkish life, but the country is very tolerant of all religions, and faiths.
Around 70% of the population is Sunni Muslims, the next largest religious group are Alevi community, who follow a nonorthodox form of Islam, and make up about 25% of the population.
Turkey has several historical mosques, the national mosque is the Sultan Ahmed Mosque (also known as the blue mosque) in Istanbul, but other notable ones include The Süleymaniye Mosque, Hagia Sofia (now a museum, formerly a mosque and before that a church) both also in Istanbul. Kocatepe Mosque in Ankara, and Alâeddin Mosque in Konya are also noteworthy, and there are also several churches and synagogues in the country.
Turkey also has several historical Christian sites, including Göreme in Cappadocia, which was the site of one of the earliest Christian settlements, and is now a major tourist attraction; mainly because the settlement was created by digging caves into the rock-face. There are many different “cave churches” in the Cappadocia region most of which feature frescoes of Christ, and these are usually from the time of the crusades.
Antioch (Antakya), the city where “the disciples were first called Christians” according to the biblical Book of Acts, is located in modern Turkey, as are most of the areas visited by St. Paul during his missions.
Turkey is fairly moderate in terms of religion, and generally a lot more relaxed about it than Middle Eastern countries, such as Iran or Syria. There is also a significant proportion of the population that class themselves as Muslim, but do not participate in religious obligations, and are maybe better classified as “believing in Islam”, than “active Muslims”.