Open-access resources offer users only two rights: access and extraction. Common property resources (CPRs), also called common pool resources, give community members the rights of access, extraction, management, and exclusion. There are many CPRs in the world. Examples include community grazing lands for cattle, community forestry, community-run irrigation systems, fishing grounds, and soil fertility under itinerant farming. Garrett Hardin argues that resources held in common are doomed to exhaustion: the tragedy of the commons. The prisoner’s dilemma is the theoretical foundation to explain the tragedy of the commons, or the non-cooperative use of a CPR. Repeated games can also lead to cooperative outcomes without explicit cooperation. To allow cooperation in managing a CPR, the resource must have well-defined boundaries and well-defined group membership, and the group must have well-defined property rights over the resource.