Contemporary economic theory is one of the more successful, empirically verified social science theories to explain human behavior. It does best, however, in the settings for which it was developed – the exchange of private goods and services in an open, competitive market. The theory is based on a theory of goods, a set of rules for social exchange, and a model of human behavior. When the goods involved are easily excludable and rivalrous, and individuals are interacting in a competitive market, theoretical predictions have strong empirical support. When the goods involved are not easy to exclude – such as public goods or common-pool resources (CPRs) – conventional theoretical predictions receive much less empirical support. In a static setting, the conventional predictions are that individuals will not produce public goods and that they will overharvest common-pool resources. The evidence for both predictions is mixed.