What is the maximum points you can win in tic-tac-toe (noughts and crosses)?

Tic-tac-toe (American English), noughts and crosses (Commonwealth English), or Xs and Os (Irish English) is a paper-and-pencil game for two players who take turns marking the spaces in a three-by-three grid with X or O. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row is the winner.

It is a solved game, with a forced draw assuming best play from both players.The game can be generalized to an m,n,k-game, in which two players alternate by placing stones of their own color on an m-by-n board with the goal of getting k of their own color in a row. Tic-tac-toe is a 3-3-3-game. Harary's generalized tic-tac-toe is an even broader generalization of tic-tac-toe. It can be generalised further by playing on an arbitrary incidence structure, where rows are lines and cells are points. Tic-tac-toe's incidence structure consists of a maximum of nine points. There are three horizontal lines, three vertical lines, and two diagonal lines, with each line consisting of three points.

Early variation of tic-tac-toe was played in the Roman Empire, around the first century BC. It was called terni lapilli (three pebbles at a time) and instead of having any number of pieces, each player had only three; thus, they had to move them around to empty spaces to keep playing. The game's grid markings have been found chalked all over Rome.