Ultimate tic-tac-toe (also known as super tic-tac-toe, strategic tic-tac-toe, or meta tic-tac-toe) is a board game composed of nine tic-tac-toe boards arranged in a 3-by-3 grid. Players take turns playing in the smaller tic-tac-toe boards until one of them wins in the larger tic-tac-toe board.

Each small 3-by-3 tic-tac-toe board is referred to as a local board, and the larger 3-by-3 board is referred to as the global board.

The game starts with X playing wherever they want in any of the 81 empty spots. This move ‘sends’ their opponent to its relative location. For example, if X played in the top right square of their local board, then O needs to play next in the local board at the top right of the global board. O can then play in any one of the nine available spots in that local board, each move sending X to a different local board.

If a move is played so that it is to win a local board by the rules of normal tic-tac-toe, then the entire local board is marked as a victory for the player in the global board.

Once the outcome of a local board is decided (win or draw), no more moves may be played in that board. If a player is sent to such a board, then that player may play in any other board.

Game play ends when either a player wins the global board or there are no legal moves remaining, in which case the game is a draw.

Ultimate Tic-tac-toe is a planned feature for Tic-tac-toe Collection. As many existing game variations as make sense will be supported, including misère and different board sizes. It may also support different rules for the global an local boards, and possibly different rules for different local boards.