Go (圍棋 weiqi in Chinese, 囲碁 igo in Japanese, 바둑 baduk in Korean, common meaning: "encircling game"), is an ancient board game for two players that originated in China more than 2,000 years ago. The game is noted for being rich in strategy despite its relatively simple rules.

The game is played by two players who alternately place black and white markers, called "stones", on the vacant intersections (called "points") of a grid of 19×19 lines (beginners often play on smaller 9×9 and 13×13 boards). The object of the game is to use one's stones to surround a larger portion of the board than the opponent. Once placed on the board, stones can only be moved if they are captured. When a game concludes, the controlled points (territory) are counted along with captured stones to determine who has more points. Games may also be won by resignation.

Go originated in ancient China; exactly when is unknown. By the 3rd century BC it was already a popular pastime, as indicated by a reference to the game in the Analects of Confucius. Archaeological evidence shows that the early game was played on a board with a 17×17 grid, but by the time the game had spread to Korea and Japan, in about the 5th and 7th centuries CE respectively, boards with a 19×19 grid had become standard.

Although the overwhelming majority of players are from East Asia, the International Go Federation has 71 member countries on all continents. The total number of players is well over 40 million. Go reached the West through Japan, which is why it is commonly known internationally by its shortened Japanese name, and why terms for common Go concepts are commonly derived from its Japanese pronunciation. The full Japanese name igo is derived from its Chinese name weiqi, which roughly translates as "board game of surrounding".