Tokyo Metro is one of two metro systems, which along with Toei, make up the Tokyo subway system. The other metro operator in Tokyo is the government of Tokyo, through the Tokyo Metropolitan Bureau of Transportation, which operates the Toei system. Metro and Toei trains form completely separate networks. While users of prepaid rail passes can freely interchange between the two networks, regular ticket holders must purchase a second ticket, or a special transfer ticket, to change from a Toei line to a Metro line and vice versa. The Tokyo Metro forms part of one of the most complex public transportation systems in the world. It is extremely well maintained and clean, although some stations on older lines are beginning to show their age.The Tokyo Metro is extremely punctual and has regular trains arriving less than five minutes apart most of the day and night. It does not however run 24 hours a day. Lines tend to stop service between midnight and 1:00am and commence again approximately 5:00am. [Extracted from Wikipedia.org]