It is played by two people who take turns marking on X or an O on a 3x3 grid. The first person to mark three of their signs in a horizontal, vertical, or diagonal row is the winner. If both players use an optimal strategy, the game will always end in a draw, and this game would become very boring and repetitive.

Most people know that playing first is best in Tictactoe: for much the same reason, achievement games in general favor the first player. There is a simple argument that, under certain conditions, achievement games favor the first player. Indeed, in these games, the first player, playing properly, cannot lose.