 Reuben and Riedl (2013) examine the enforcement of norms of contribution to public goods in homogeneous and heterogeneous groups, such as groups whose members vary in their endowment, contribution capacity, or marginal benefits. In particular, Reuben and Riedl are interested in the normative appeal of two potentially applicable rules: the efficiency rule (prescribing maximal contributions by all) and the class of relative contribution rules (prescribing a contribution that is “fair” relative to the contributions of others; e.g., equality and equity rules). Reuben and Riedl’s results show that, in the absence of punishment, no positive contribution norm emerged and all groups converged toward free-riding. By contrast, with punishment, contributions were consistent with the prescriptions of the efficiency rule in a significant subset of groups (irrespective of the type of group heterogeneity); in other groups, contributions were consistent with relative contribution rules. These results suggest that even in heterogeneous groups individuals can successfully enforce a contribution norm. Most notably, survey data involving third parties confirmed well-defined yet conflicting normative views about the aforementioned contribution rules; in other words, both efficiency and relative contribution rules are normatively appealing, and are indeed potential candidates for emerging contribution norms in different groups.