To play tic-tac-toe, two players take turns placing either an X or an O into the spaces of a three-by-three grid until one player gets three in a row. If the players fill all squares with no one getting three in a row, the round is a draw.
Players can flip a coin to see who gets to place Xs and who gets to play Os, and the one with X always goes first. A winning set of three letters in a row may be horizontal, vertical or diagonal. To play tic-tac-toe on a four-by-four grid, the same rules apply except that both players try to get four of their letters in a row, and the game is a draw if all 16 squares become filled.
Increasing the size of the grid increases the game's difficulty as every game on a three-by-three grid nearly always results in a draw if both players are playing skillfully. Players can play tic-tac-toe on a five-by-five, 10-by-10 or even 20-by-20 grid. For grids larger than six-by-six, players may wish to stick to a goal of five in a row to make the game easier to win. This more complex version of the game is similar to games such as pente.