 In the iterated Prisoner’s Dilemma, players repeat their interactions, either in a fixed number of rounds or in an infinite or indefinite repetition. Robert Axelrod’s tournaments in the early 1980s are the classic studies in the iterated prisoner’s dilemma, and early examples of the application of computational techniques. Strategies for playing the Prisoner’s Dilemma were solicited from experts in various fields, pitted against all others (and themselves) in round-robin competition over 200 rounds. Famously, the strategy that triumphed was Tit for Tat, a simple strategy which responds to cooperation from the other player on the previous round with cooperation, responding to defection on the previous round with defection. Even more surprisingly, Tit for Tat again came out in front in a second tournament, despite the fact that submitted strategies knew that Tit for Tat was the opponent to aim for. When those same strategies were explored with replicator dynamics in place of round-robin competition, Tit for Tat again was the winner (Axelrod and Hamilton 1981). Further work has tempered Tit for Tat’s reputation somewhat, emphasizing the constraints of Axelrod’s tournaments both in terms of structure and the strategies submitted (Kendall, Yao, &amp; Chang 2007; Kuhn 1997 [2019]).