Go is an abstract strategy board game for two players in which the aim is to surround more territory than the opponent. The game was invented in China more than 4,500 years ago and is believed to be the oldest board game continuously played to the present day. Despite its relatively simple rules, Go is extremely complex. Compared to chess, Go has both a larger board with more scope for play and longer games and, on average, many more alternatives to consider per move. The number of legal board positions in Go has been calculated to be approximately 2.1×10^170, which is far greater than the number of atoms in the observable universe, estimated to be of the order of 10^80.

Source: Wikipedia