Istanbul (Turkish: ?stanbul), historically known as Byzantium and Constantinople, is the largest city of Turkey. Istanbul metropolitan province (municipality) had 13.26 million people living in it as of December, 2010, which is 18% of Turkey's population and the 3rd largest metropolitan area in Europe (including the Asian side of the city) after London and Moscow.

Istanbul is a megacity, the cultural, economic, and financial center of Turkey. Located in the northwest of the country, it lies on the Bosphorus strait and encompasses the natural harbour known as the Golden Horn. Extending both on the European (Thrace) and Asian (Anatolia) sides of the strait, it is the only metropolis in the world situated on two continents. In 2010, it has been ranked by GaWC as an alpha(-) world city.

During its long history, Istanbul has served as the capital of the Roman Empire (330-395), the Eastern Roman (Byzantine) Empire (395-1204 and 1261-1453), the Latin Empire (1204-1261), and the Ottoman Empire (1453-1922). When the Republic of Turkey was proclaimed on 29 October 1923, Ankara, which had previously served as the headquarters of the Turkish national movement during the Turkish War of Independence, was chosen as the new Turkish State's capital.

Istanbul was named a joint European Capital of Culture for 2010 and the European Capital of Sports for 2012. Istanbul is currently bidding to host the 2020 Summer Olympics. The historic areas of the city were added to the UNESCO World Heritage List in 1985. The city covers 39 districts of the Istanbul province.