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 2,500 years ago and is believed to be one of the oldest board games continuously played to the present day. A 2016 survey by the International Go Federation's 75 member nations found that there are over 46 million people worldwide who know how to play Go and over 20 million current players, the majority of whom live in East Asia.

The playing pieces are called stones. One player uses the white stones and the other, black. The players take turns placing the stones on the vacant intersections of a board. Once placed on the board, stones may not be moved, but stones are removed from the board if "captured". Capture happens when a stone or group of stones is surrounded by opposing stones.The game proceeds until neither player wishes to make another move. When a game concludes, the winner is determined by counting each player's surrounded territory along with captured stones. 

The standard Go board has a 19×19 grid of lines, containing 361 points. Beginners often play on smaller 9×9 and 13×13 boards,and archaeological evidence shows that the game was played in earlier centuries on a board with a 17×17 grid. However, boards with a 19×19 grid had become standard by the time the game had reached Korea in the 5th century CE and later Japan in the 7th century CE.

A player may not place a stone such that it or its group immediately has no liberties, unless doing so immediately deprives an enemy group of its final liberty. In the latter case, the enemy group is captured, leaving the new stone with at least one liberty.This rule is responsible for the all-important difference between one and two eyes: if a group with only one eye is fully surrounded on the outside, it can be killed with a stone placed in its single eye.

Playing with others usually requires a knowledge of each player's strength, indicated by the player's rank (increasing from 30 kyu to 1 kyu, then 1 dan to 7 dan, then 1 dan pro to 9 dan pro). A difference in rank may be compensated by a handicap—Black is allowed to place two or more stones on the board to compensate for White's greater strength.There are different rule-sets, which are almost entirely equivalent, except for certain special-case positions.