CLAMP is a group of four women who have become one of the most popular manga artists in the world - Satsuki Igarashi, Mick Nekoi, Mokona Apapa and Nanase Ohkawa. They started out as doujnishi (fan comics) creators, but their skill and craft brought them to the attention of publishers very quickly. Their first work from a major publisher was RG Veda, but their first mass success was with Magic Knight Rayearth. From there, they went on to write many series, including Cardcaptor Sakura and Chobits, two of the most popular manga available. Like many Japanese manga artists, they prefer to avoid the spotlight, and little is known about them personally.
CLAMP is also the author of Tsubasa, another title brought to you by Tanoshimi.