Basic rules

* Two players, Black and White, take turns placing a stone (game piece) on a vacant point (intersection) of a 19 by 19 board (grid). Black moves first. Other board sizes such as 13x13 and 9x9 may be used for teaching or quick games, but 19x19 is the standard size. Once played, a stone may not be moved to a different point.
* A vacant point adjacent to a stone is a liberty for that stone.
* Adjacent stones of the same color form a chain (also called a group) that shares its liberties in common, cannot subsequently be subdivided, and in effect becomes a single larger stone. Only stones connected to one another by the lines on the board create a chain.
* Chains may be expanded by playing additional stones of the same color on their liberties, or amalgamated by playing a stone on a mutual liberty of two or more chains of the same color.
* A chain must have at least one liberty to remain on the board. When a chain is surrounded by opposing stones so that it has no liberties, it is captured and removed from the board.
* If a stone is played where it has no liberties, but it occupies the last liberty of one or more opposing chains, then such chains are captured first, leaving the newly played stone at least one liberty.
* "Ko rule": A stone cannot be played on a particular point, if doing so would recreate the board position that existed after the same player's previous turn.
* A player may pass instead of placing a stone, indicating that he sees no way to increase his territory or reduce his opponent's territory. When both players pass consecutively, the game ends and is then scored.

A player's score is the number of empty points enclosed by his stones plus the number of opposing stones which he has captured. Points which are occupied by stones do not count for scoring purposes. The player with the higher score wins. (Note that there are other rule sets that count the score differently, yet almost always produce the same result.) For a more detailed treatment, see Rules of Go.

This is the essence of the game of Go. The risk of capture means that stones must work together to control territory, which makes the gameplay very complex and interesting.
If white plays at A, the black chain loses its last liberty, and is captured and removed from the board.
If white plays at A, the black chain loses its last liberty, and is captured and removed from the board.

Go allows one to play not only even games (games between players of roughly equal strength) but also handicap games (games between players of unequal strength). Without a handicap, even a slight difference in strength will generally be decisive.

Optional rules

Optional Go rules may set the following:

* compensation points, almost always for the second player, see komi;
* compensation stones placed on the board before alternate play, allowing players of different strengths to play competitively (see Go handicap for more information);
* "superko": the ko rule (a move must not recreate the previous position) is extended to disallow any previous position. This prevents complex repetitive situations ("triple ko", "eternal life", etc.) from cycling indefinitely.