The Tokyo metropolis is made up of 23 special wards, or "tokubetsuku" (特別区). The word "special" separates the Tokyo wards from those in other major Japanese cities. Each ward handles certain functions (water and sewage, for example) within its area while at the same time working together with the other special wards to provide other services (such as mail delivery, taxation, etc.).
Foreigners living in Tokyo must register with the ward head office whenever they move from ku to ku.