In game theory, perfect play by a player is the behavior or strategy which leads to the best possible outcome for that player.

Perfect play is only meaningful only in scenarios with perfect information and no chance, since otherwise it is impossible to determine with certainty what the outcome of a given strategy will be.

In practice, the optimal strategy might be impossible to determine even when there is perfect information, since there might be too many possibilities for a human or even a computer to exhaustively analyze. This is the case in games such as chess. In such cases the notion of perfect play mainly serves as a yardstick to measure practical strategies or algorithms.

On the other hand, we can say that the game of tic tac toe ends in a tie with perfect play by both sides. Games like nim also admit of a rigorous analysis using combinatorial game theory.

See also: Solved board games.