Istanbul Province (Turkish: İstanbul ili) is a province located in north-west Turkey. It has an area of 5,343.02 km² and a population of 13,255,685. The population was 10,018,735 in 2000. It is surrounded by the provinces of Tekirdağ to the west, Kocaeli to the east, the Black Sea to the northern part and the Sea of Marmara to the south. The Bosphorus (Boğaziçi) Strait divides the province in two parts: the European side and the Asian side. Roughly 3.85 million people live on the Asian side in 2010 census, and 9.4 million on the European side.

The capital of the province is the city of Istanbul, which, since 2004, has the same boundaries as the province.

The province also includes the Princes' Islands constituted as Adalar District (Island District).