The Shannon number, named after the American mathematician Claude Shannon, is a conservative lower bound of the game-tree complexity of chess of 10120, based on an average of about 103 possibilities for a pair of moves consisting of a move for White followed by a move for Black, and a typical game lasting about 40 such pairs of moves.

Claude Elwood Shannon was an American mathematician, electrical engineer, computer scientist and cryptographer known as the "father of information theory". He was the first to describe the Boolean gates that are essential to all digital electronic circuits, and he built the first machine learning device, thus founding the field of artificial intelligence. He is credited alongside George Boole for laying the foundations of the Information Age.