Many imminent problems facing the world today, such as deforestation, overfishing, or climate change, can be described as 'commons problems.' The solution to these problems requires cooperation from hundreds and thousands of people. Such large scale cooperation, however, is plagued by the infamous cooperation dilemma. According to the standard prediction, in which each individual follows only his own interests, large-scale cooperation is impossible because free-riders enjoy common benefits without bearing the cost of their provision. Yet, extensive field evidence indicates that many communities are able to manage their commons, albeit with varying degrees of success.ScienceDaily