Tokyo (東京 ,Tōkyō?), officially Tokyo Metropolis (東京都 ,Tōkyō-to?), is one of the 47 prefectures of Japan and 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, totalling 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 is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family.

Source: Wikipedia