Many problems of the human society, such as overexploiting fish stock or the difficulty of sustaining the global climate, are problems of achieving cooperation. When individuals, groups or states are free to overuse a public good they usually overuse it. Thus, public goods are at risk to collapse, which happens to health insurance systems, fish stock and probably the global climate. This problem that is known as the "tragedy of the commons" , has been studied intensively by social- and political scientists and economists since decades and recently by evolutionary biologists. Except for allowing for punishing defectors , no scenario that facilitates a cooperative solution of the tragedy of the commons has been found yet. Scientists from the Max Planck Institute of Limnology could show that an unexpectedly efficient solution of the problem can be achieved when personal reputation, which is important for other social interactions, is at stake in the public goods situation. When this interaction is allowed for, the public good is not only sustained but also provides all participants with a high payoff .