A game-theory mechanism which is subject to a payoff matrix similar to that of a prisoner’s dilemma. Tit for tat was introduced by Robert Axelrod, who developed a strategy where each participant in an iterated prisoner’s dilemma will follow a course of action which is consistent with their opponent’s previous turn. For example, if provoked, a player will subsequently respond with retaliation, but if they are not provoked, the player will subsequently cooperate.

Tit-for-tat strategies are based on the concepts of retaliation and altruism. When faced with a prisoner’s dilemma-like scenario, an individual will cooperate when the other member has an immediate history of cooperating and will default when the counterparty previously defaulted.

This concept is often applied to economics and biology.