Go

Board

Go is a 2-player game usually played on a board of 19 horizontal and 19 vertical lines, as shown below.

One player uses a set of black stones; the other player uses a set of white stones.

Counting & Winning

Players alternately play stones on any "neutral" points--intersections adjacent to both players' stones, also known as "dame" (pronounced DAH-MAY). Next, "dead" stones--ones that are not fully surrounded, but that would inevitably be captured if play continued--are removed from the board and added to the piles of prisoners. Finally, players add up their scores. A player earns one point for each vacant intersection surrounded by his or her stones--known as the player's "territory"--and one point for each prisoner he or she has captured. Whoever has more points wins.

In the position on the board below, the four points marked X are dame--worthless to either side.

After removing the dead White stone inside Black's upper right territory, Black has 7 points in the upper right, 2 points in the lower left, and 1 for the removed prisoner, for a total of 10. White has 5 points in the upper left, 2 in the lower right, and 2 for the captured Black stones, a total of 9. Black wins by 1 point (unless he or she is required to give White compensation, or komi, to offset the advantage of going first, as explained below).

If a player had to surround them completely, he or she would lose one point for each intersection that was filled in while surrounding them. In the previous example, Black would need to play two stones inside Black territory to remove the dead White stone in the upper right, changing the outcome of the game. Therefore, the rules allow players to simply remove dead stones after both players have passed and neutral points have been filled in.

Placing Stones

Beginning with Black, each player in turn places a stone on an empty intersection, or "point." Once placed, a stone is never moved, although it is removed if the opponent captures it.

If any stones become completely surrounded by opposing pieces, they are captured and removed, as shown in the example of the White stone below.

A stone or group is completely surrounded when it is not adjacent--in any horizontal or vertical direction--to any empty intersections.

Seki

Occasionally, adjacent opposing groups will become surrounded while neither group has two eyes. If one group has enough extra liberties, it may be able to capture the other. Otherwise, a seki, or dual life, is a likely result of the battle.

In the below picture, the White group in the lower left has two eyes, and so is safe. The two Black groups in the corners at the top have just one eye each (the corner points), but are safe because White cannot play on either point marked X without allowing Black to capture the White stones. Meanwhile, the five White stones on the right and the large Black group at the bottom are both eyeless, but both groups are safe because neither player can occupy either of the points marked Y without allowing the opponent to play on the other point Y and capture them. Since neither player can approach the other anywhere, the various groups with fewer than two eyes are alive in seki.

Ko

In the below picture, Black can capture one White stone by playing at X. The resulting position is shown. If White plays at Y, the former arrangement is restored. However, White may not make such a move without playing somewhere else first, thus giving Black a chance to play at Y and retain the captured point.

Suicide Moves

A stone may not be placed in such a way that it (or the group it's part of) has no liberties. (Chinese rules allow such "suicide" moves; the stone that was just played (or the group it's part of) is captured right away; occasionally, such a move can be useful as a ko threat.

This is illustrated by the below position, in which a White move at X would cause two White stones to be removed, but White would now threaten to play at X again, making Black's eye to the left of X a false eye.