2. Hardin's 'Tragedy of the Commons' model predicts the eventual overexploitation or degradation of all resources used in common. Given this unambiguous prediction, a surprising number of cases exist in which users have been able to restrict access to the resource and establish rules among themselves for its sustainable use. Evidence accumulated over the last twenty-two years indicates that private, state, and communal property are all potentially viable resource management options. A more complete theory than Hardin's should incorporate institutional arrangements and cultural factors to provide for better analysis and prediction.