Common pool resources (CPRs) are resources for which the exclusion of prospective users is difficult and whose utilization by one person affects the availability or quality of the resource for others (a property known in the literature as subtractability). Examples of CPRs include pastures, fishing grounds, irrigation systems, groundwater basins, forests, atmosphere, wildlife, and, more recently, biodiversity and the “digital commons.” CPRs contrast with private goods, where exclusion is feasible, and public goods, which do not exhibit subtractability. The management challenge of CPRs derives from the resultant user incentives. The benefits of exploitation tend to accrue to individual users, but the costs of use, in terms of a reduced resource base or higher extraction costs, are spread among all users. At the same time, the ...