Rules of Go

Go is played on a square board with black and white stones. Professional games are played on a 19x19 board; faster games can be played on smaller boards like 9x9 or 13x13.

• The game starts with the empty board; the object of the game is to control more board points than the opponent at the end of the game.
• Black plays first; the players move alternately by placing a stone of their color on an empty point.
• Once played, stones are never moved, but they may be captured if they're completely surrounded by opponent stones.

End of game

A player can pass at any time; the game ends when both players pass. The occupied points as well as the points completely surrounded by a player count as their area; the player with the most area wins the game.

Handicap and Komi

To compensate for differences in strength, the weaker player may start with a handicap of two or more stones. In even games, White gets extra points (komi) to compensate for Black's advantage of playing first. The komi usually includes a half point to avoid draws.

Capture

Stones that are completely surrounded are captured and removed from the board. For example, White can play at A to capture the black stone.

Blocks of stones connected vertically or horizontally fight together and are captured as a unit. For example, White playing at A will capture three stones:

Ko

You're not allowed to repeat previous board positions; the rule of ko prohibits you from playing a move that would cause the position to be repeated.

In the above example, you can't capture back immediately. However, you can re-capture after moves are played elsewhere on the board. So you can play a threat elsewhere and then take back after the opponent answers your threat.

Suicide

Moves that end up being completely surrounded are forbidden. Two examples:

Both A and B are suicide for Black: The black stones would end up completely surrounded. However, Black can play at C, as that would capture two white stones: