Istanbul is a metropolis inhabited by many people of different cultures and religions. The largest portion of the population is Muslim. Religious minorities include Greek Orthodox, Armenian Orthodox, and Sephardic and Ashkenazi Jews.

Although the population of religious minorities has decreased as a result of wars and other political and cultural changes, they are still found in specific districts. For example Armenians are in the majority in Kumkapı, Jews in Balat and Greek Orthodox in Fener.

According to the 2000 census Istanbul, which is home to the Greek Orthodox Patriarchate, has 2,691 active mosques, 123 active churches and 26 active synagogues.