 One of the most widely utilized solution concepts is the Nash equilibrium. Based upon the Bayesian rationality criterion according to which one chooses so as to maximize her expected utility, a Nash equilibrium is a profile of strategies adopted by a set of agents in which the strategy adopted by each agent maximizes her respective payoff given the probabilistically independent strategies adopted by other agents. In other words, at a Nash equilibrium each agent’s strategy is a best response to the others’ strategies, so that none can do better by acting differently given what others are doing. Although Nash was not the first to introduce this equilibrium concept, its broad applicability was recognized only after Nash refined the concept and proved that if a noncooperative game has finitely many pure strategy profiles, then at least one Nash equilibrium always exists. Prior to Nash’s proof it was widely known that many games lack a Nash equilibrium in pure strategies where each agent optimally responds to what every other agent does by adopting one of the actions available to her. This initially limited the class of problems to which the concept could be applied, but Nash showed that in such cases there will always be a Nash equilibrium in mixed strategies were each agent optimally responds to what other agents do by choosing among a subset of the strategies available to her with some probability. The usefulness of this concept would then be further extended by subsequent refinements, including most notably those made by John Harsanyi and Reinhard Selten (see, e.g., Harsanyi &amp; Selten 1988).