Baku (Azerbaijani: Bakı, IPA: [bɑˈcɯ]), sometimes spelled as Baki or Bakou, is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea and of the Caucasus region. It is located on the southern shore of the Absheron Peninsula, which projects into the Caspian Sea. The city consists of two principal parts: the downtown and the old Inner City (21.5 ha). Baku's urban population at the beginning of 2009 was estimated at just over two million people. Officially, about 25 percent of all inhabitants of the country live in the metropolitan city area of Baku.

Baku is divided into eleven administrative districts (raions) and 48 townships. Among these are the townships on islands in the Baku Bay and the town of Oil Rocks built on stilts in the Caspian Sea, 60 km (37 mi) away from Baku. The Inner City of Baku along with the Shirvanshah's Palace and Maiden Tower were inscribed as a UNESCO World Heritage Site in 2000. According to the Lonely Planet's ranking, Baku is also among the world's top ten destinations for urban nightlife.