We develop a theory of resource management where the degree to which countries escape the tragedy of the commons, and hence the de facto property rights regime, is endogenously determined. Three forces determine success or failure in resource management: the regulator's enforcement power, the extent of harvesting capacity, and the ability of the resource to generate competitive returns without being extinguished. The model can explain heterogeneity across countries and resources in the e¤ectiveness of resource management, and it predicts that changes in prices, population, and technology can cause transitions to better or worse management regimes. Policy analysis based on the assumption of a …xed degree of property rights protection may lead to serious error.We are grateful to many people for comments on earlier versions, and participants at