The game is played on an 8x8 grid (though any size is possible). One player secretly chooses a grid row and the other secretly chooses a grid column. Players then take turns to place a piece on any square of the board, and the winner is the player who places a piece at the intersection between the chosen row and column. The game is extremely psychological, involving neither chance nor strategy beyond trying to second-guess your opponent's thinking.
Since each player can know only one of the two pieces of information needed to determine the winner, the game currently requires either a neutral referee or a playing set (designed with the assistance of Darien Graham-Smith) to indicate mechanically when a piece is placed at the intersection.