This paper by B. Douglas Bernheim explores the nature of rational choice in strategic games, challenging the notion that rationality alone requires agents to select a Nash equilibrium strategy. Bernheim introduces the concept of "rationalizable" strategies, which are those that can be justified by a consistent system of beliefs. He argues that no rationalizable strategy can be discarded based solely on rationality, and all rationally justifiable strategies are members of the rationalizable set. The paper studies the properties of rationalizable strategies and considers various refinements to the criterion, including the relationship between rationalizable and Nash strategies. Bernheim also examines the topological properties of rationalizable strategies, noting that multiplicity can be a severe problem. He concludes by discussing refinements to the rationalizability criterion, such as the "trembling hand perfectness" and "cautious rationalizability," which aim to eliminate undesirable strategies like weakly dominated choices.This paper by B. Douglas Bernheim explores the nature of rational choice in strategic games, challenging the notion that rationality alone requires agents to select a Nash equilibrium strategy. Bernheim introduces the concept of "rationalizable" strategies, which are those that can be justified by a consistent system of beliefs. He argues that no rationalizable strategy can be discarded based solely on rationality, and all rationally justifiable strategies are members of the rationalizable set. The paper studies the properties of rationalizable strategies and considers various refinements to the criterion, including the relationship between rationalizable and Nash strategies. Bernheim also examines the topological properties of rationalizable strategies, noting that multiplicity can be a severe problem. He concludes by discussing refinements to the rationalizability criterion, such as the "trembling hand perfectness" and "cautious rationalizability," which aim to eliminate undesirable strategies like weakly dominated choices.