Istanbul has been a cosmopolitan city throughout much of its history, but it has become more homogenized since the end of the Ottoman Empire.
The vast majority of people across Turkey, and in Istanbul, are Muslim, and more specifically members of the Sunni branch of Islam.
Most Sunni Turks follow the Hanafi school of Islamic thought, while Sunni Kurds tend to follow the Shafi'i school.
The largest non-Sunni Muslim group, accounting 10–20% of Turkey's population, are the Alevis; a third of all Alevis in the country live in Istanbul.
Mystic movements, like Sufism, were officially banned after the establishment of the Turkish Republic, but they still boast numerous followers.
Istanbul is a migrant city.
Since the 1950s, Istanbul's population has increased from 1 million to about 10 million residents.
Almost 200,000 new immigrants, many of them from Turkey's own villages, continue to arrive each year.
As a result, the city constant change, constantly reshaped to achieve the needs of these new population.

The Patriarch of Constantinople has been designated Ecumenical Patriarch since the sixth century, and has come to be regarded as the leader of the world's 300 million Orthodox Christians.
Since 1601, the Patriarchate has been based in Istanbul's Church of St. George.
Into the 19th century, the Christians of Istanbul tended to be either Greek Orthodox, members of the Armenian Apostolic Church or Catholic Levantines.
Because of events during the 20th century—including the 1923 population exchange between Greece and Turkey, a 1942 wealth tax, and the 1955 Istanbul riots—the Greek population, originally centered in Fener and Samatya, has decreased substantially.
At the start of the 21st century, Istanbul's Greek population numbered 3,000 (down from 260,000 out of 850,000 according to the Ottoman Census of 1910, and a peak of 350,000 in 1919).
There are today between 50,000 and 90,000 Armenians in Istanbul, down from about 164,000 according to the Ottoman Census of 1913 (partly due to the Armenian Genocide).
The Levantines, Latin Christians who settled in Galata during the Ottoman period, played a seminal role in shaping the culture and architecture of Istanbul during the 19th and early 20th centuries; their population has dwindled, but they remain in the city in small numbers.

The largest ethnic minority in Istanbul is the Kurdish community, originating from eastern and southeastern Turkey.
Although the Kurdish presence in the city dates back to the early Ottoman period, the influx of Kurds into the city has accelerated since the beginning of the Kurdish–Turkish conflict in the late 1970s.
Between two and four million residents of Istanbul are Kurdish, meaning there are more Kurds in Istanbul than in any other city in the world.
There are other significant ethnic minorities as well, the Bosniaks are the main people of an entire district – Bayrampaşa.
The neighborhood of Balat used to be home to a sizable Sephardi Jewish community, first formed after their expulsion from Spain in 1492.
Romaniotes and Ashkenazi Jews resided in Istanbul even before the Sephardim, but their proportion has since dwindled; today, 1 percent of Istanbul's Jews are Ashkenazi.
In large part due to emigration to Israel, the Jewish population nationwide dropped from 100,000 in 1950 to 18,000 in 2005, with the majority of them living in either Istanbul or İzmir.
From the increase in mutual cooperation between Turkey and several African States like Somalia and Djibouti, several young students and workers have been migrating to Istanbul in search of better education and employment opportunities.
There are Nigerian, Congolese and Cameroonian communities present.
Istanbul has been a cosmopolitan city throughout much of its history, but it has become more homogenized since the end of the Ottoman Empire. The vast majority of people across Turkey, and in Istanbul, are Muslim, and more specifically members of the Sunni branch of Islam. Most Sunni Turks follow the Hanafi school of Islamic thought, while Sunni Kurds tend to follow the Shafi'i school. The largest non-Sunni Muslim group, accounting 10–20% of Turkey's population, are the Alevis; a third of all Alevis in the country live in Istanbul. Mystic movements, like Sufism, were officially banned after the establishment of the Turkish Republic, but they still boast numerous followers. Istanbul is a migrant city. Since the 1950s, Istanbul's population has increased from 1 million to about 10 million residents. Almost 200,000 new immigrants, many of them from Turkey's own villages, continue to arrive each year. As a result, the city constant change, constantly reshaped to achieve the needs of these new population.
The Patriarch of Constantinople has been designated Ecumenical Patriarch since the sixth century, and has come to be regarded as the leader of the world's 300 million Orthodox Christians. Since 1601, the Patriarchate has been based in Istanbul's Church of St. George. Into the 19th century, the Christians of Istanbul tended to be either Greek Orthodox, members of the Armenian Apostolic Church or Catholic Levantines. Because of events during the 20th century—including the 1923 population exchange between Greece and Turkey, a 1942 wealth tax, and the 1955 Istanbul riots—the Greek population, originally centered in Fener and Samatya, has decreased substantially. At the start of the 21st century, Istanbul's Greek population numbered 3,000 (down from 260,000 out of 850,000 according to the Ottoman Census of 1910, and a peak of 350,000 in 1919). There are today between 50,000 and 90,000 Armenians in Istanbul, down from about 164,000 according to the Ottoman Census of 1913 (partly due to the Armenian Genocide). The Levantines, Latin Christians who settled in Galata during the Ottoman period, played a seminal role in shaping the culture and architecture of Istanbul during the 19th and early 20th centuries; their population has dwindled, but they remain in the city in small numbers.
The largest ethnic minority in Istanbul is the Kurdish community, originating from eastern and southeastern Turkey. Although the Kurdish presence in the city dates back to the early Ottoman period, the influx of Kurds into the city has accelerated since the beginning of the Kurdish–Turkish conflict in the late 1970s. Between two and four million residents of Istanbul are Kurdish, meaning there are more Kurds in Istanbul than in any other city in the world. There are other significant ethnic minorities as well, the Bosniaks are the main people of an entire district – Bayrampaşa. The neighborhood of Balat used to be home to a sizable Sephardi Jewish community, first formed after their expulsion from Spain in 1492. Romaniotes and Ashkenazi Jews resided in Istanbul even before the Sephardim, but their proportion has since dwindled; today, 1 percent of Istanbul's Jews are Ashkenazi. In large part due to emigration to Israel, the Jewish population nationwide dropped from 100,000 in 1950 to 18,000 in 2005, with the majority of them living in either Istanbul or İzmir. From the increase in mutual cooperation between Turkey and several African States like Somalia and Djibouti, several young students and workers have been migrating to Istanbul in search of better education and employment opportunities. There are Nigerian, Congolese and Cameroonian communities present.
Istanbul