Tokyo (東京, Tōkyō?), officially Tokyo Metropolis (東京都, Tōkyō-to?),[2] is one of the 47 prefectures of Japan and is located on the eastern side of the main island Honshū. The twenty-three special wards of Tokyo, each governed as a city, cover the area that was once the city of Tokyo in the eastern part of the prefecture, totaling over 8 million people. The population of the prefecture exceeds 12 million. The prefecture is the center of the Greater Tokyo Area, the world's most populous metropolitan area with 35 million people and the world's largest metropolitan economy with a GDP of US$1.191 trillion at purchasing power parity in 2005.
Tokyo was described by Saskia Sassen as one of the three "command centers" for the world economy, along with London and New York City.[3] This city is considered an alpha+ world city, listed by the GaWC's 2008 inventory[4] and ranked fourth among global cities by Foreign Policy's 2008 Global Cities Index. In 2009 Tokyo was named the world's most expensive city for expatriate employees, according to the Mercer Human Resource Consulting and Economist Intelligence Unit cost-of-living surveys [5] and named the third Most Liveable City and the Worlds Most Livable Megalopolis by international lifestyle magazine Monocle.
Tokyo is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family.

東京為位於日本本州島東部的都市。明治維新後即成為日本的實質首都所在地至今，同時也是日本政治、經濟、文化、交通等的中心。

在正式的行政區劃定義上，東京指的是東京都。有關對於東京（有時包括周邊地區在內）的各種稱呼所指涉的範圍，以及東京都的行政區劃範圍，請參見下方的定義與行政區段落。