 According to some authors, we can explain the emergence of norms without any reference to the functions they eventually come to perform. Since the norms that are most interesting to study are those that emerge naturally from individuals’ interactions (Schelling 1978), an important theoretical task is to analyze the conditions under which such norms come into being. Because norms often provide a solution to the problem of maintaining social order—and social order requires cooperation—many studies on the emergence and dynamics of norms have focused on cooperation. Norms of honesty, loyalty, reciprocity and promise-keeping are indeed important to the smooth functioning of social groups. One hypothesis is that such cooperative norms emerge in close-knit groups where people have ongoing interactions with each other (Hardin 1982). Evolutionary game theory provides a useful framework for investigating this hypothesis, since repeated games serve as a simple approximation of life in a close-knit group (Axelrod 1984, 1986; Skyrms 1996; Gintis 2000). In repeated encounters people have an opportunity to learn from each other’s behavior, and to secure a pattern of reciprocity that minimizes the likelihood of misperception. In this regard, it has been argued that the cooperative norms likely to develop in close-knit groups are simple ones (Alexander 2000, 2005, 2007); in fact, delayed and disproportionate punishment, as well as belated rewards, are often difficult to understand and hence ineffective. Although norms originate in small, close-knit groups, they often spread well beyond the narrow boundaries of the original group. The challenge thus becomes one of explaining the dynamics of the norm propagation from small groups to large populations.