[b]Clamp[/b], also known as CLAMP, is an all-female Japanese mangaka group. Their manga series are often made into anime after release. More than 90 million Clamp tankoubon copies have been sold worldwide.
Clamp originally began in 1989 as a twelve-member doujinshi circle. The former members of Clamp included Tamayo Akiyama, Soushi Hishika, O-Kyon, Kazue Nakamori, Yuzuru Inoue, Sei Nanao, Shinya Ohmi and Leeza Sei. By 1990, the circle had diminished from twelve to seven. Of the remaining seven, Tamayo Akiyama, Sei Nanao, and Leeza Sei left the group over the course of RG Veda's production, leaving the current four members.
According to Clamp, the group's name means "a pile of potatoes".
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http://en.wikipedia.org/wiki/CLAMP