Tokyo (東京, Tōkyō; "Eastern Capital"), officially Tokyo Metropolis (東京都, Tōkyō-to), is one of the 47 prefectures of Japan. It is located on the eastern side of the main island Honshū and includes the Izu Islands and Ogasawara Islands. Tokyo Metropolis was formed in 1943 from the merger of the former Tokyo Prefecture (Tokyo-fu) and the city of Tokyo. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family.

The Tokyo Metropolitan government administers the twenty-three special wards of Tokyo, each governed as a city, that cover the area that was the city of Tokyo as well as 39 municipalities in the western part of the prefecture and the two outlying island chains. The population of the special wards is over 8 million people, with the total population of the prefecture exceeding 13 million. The prefecture is part of the world's most populous metropolitan area with 35 to 39 million people (depending on definition) and the world's largest metropolitan economy with a GDP of US$1.479 trillion at purchasing power parity in 2008.

Tokyo was described by Saskia Sassen as one of the three "command centers" for the world economy, along with New York City and London. This city is considered an alpha+ world city, listed by the GaWC's 2008 inventory 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 and Economist Intelligence Unit cost-of-living surveys and named the third Most Liveable City and the World’s Most Livable Megalopolis by the magazine Monocle.