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Demographics

Throughout most of its history, Istanbul has ranked among the largest cities in the world. By 500 CE, Constantinople had somewhere between 400,000 and 500,000 people, edging out its predecessor, Rome, for the world's largest city. Constantinople jostled with other major historical cities, such as Baghdad, Chang'an, Kaifeng and Merv for the position of the world's largest city until the 12th century. It never returned to being the world's largest, but remained the largest city in Europe from 1500 to 1750, when it was surpassed by London.

The Turkish Statistical Institute estimates that the population of Istanbul Metropolitan Municipality was 15,519,267 at the end of 2019, hosting 19 percent of the country's population. 64.4% of the residents live on the European side and 35.6% on the Asian side.

Istanbul ranks as the seventh-largest city proper in the world, and the second-largest urban agglomeration in Europe, after Moscow. The city's annual population growth of 1.5 percent ranks as one of the highest among the seventy-eight largest metropolises in the Organisation for Economic Co-operation and Development. The high population growth mirrors an urbanization trend across the country, as the second and third fastest-growing OECD metropolises are the Turkish cities of İzmir and Ankara.

Istanbul experienced especially rapid growth during the second half of the 20th century, with its population increasing tenfold between 1950 and 2000. This growth was fueled by internal and international migration. Istanbul's foreign population with a residence permit increased dramatically, from 43,000 in 2007 to 856,377 in 2019.

According to 2020 TÜİK data around 2.1 million people in a population of over 15.4 million have been registered in Istanbul, meanwhile the vast majority of the residents ultimately originate from Anatolian provinces, especially those in the Black Sea, Central and Eastern Anatolia regions due to internal migration since the 1950s. People registered in Kastamonu, Ordu, Giresun, Erzurum, Samsun, Malatya, Trabzon, Sinop and Rize provinces represent the biggest population groups in Istanbul, meanwhile people registered in Sivas has the highest percentage with more than 760 thousand residents in the city. A 2019 survey found that only 36% of the Istanbul's population was born in the province.