From the back of the box:
FOURSIGHT - a classic game for two, is the only board game that actually allows you to play half of your opponent's pieces as well as your own. To win, you must learn to think like your opponent and have the foresight to change your strategy as conditions of play change. Your object: get 4 in a row to win immediately or three in a row four times. Colored scoring pieces may only be played on neutral (foundation) pieces. Plan your strategy well, because once you've placed your pieces on the board, they can't be moved.
FOURSIGHT combines the simplicity of tic-tac-toe with the challenge of chess for a game of infinite variations.