Ultimate Tic-Tac-Toe is an advanced form of Tic-Tac-Toe, where each square in the 3 x 3 board contains a smaller Tic-Tac-Toe game. In order to put your X in a square on the grid, you must win the mini-board game that square contains. But there is an additional complication: you don’t get to pick which board in the 3 x 3 grid you get to play on. That is determined by your opponent’s previous move. Whichever square he played on, that is the board you must play on when it’s your turn.