Global common resources like international airspace and the high seas are in danger of overexploitation because the users need not bear the full social costs of their actions. The CO2-emissions of international aviation and of shipping are not subject to the quantitative reduction obligations of the Kyoto Protocol. Imposing user charges can close this regulatory gap and induce environment-related incentive effects to reduce environmental damage. Moreover, additional financial resources are generated, which should be earmarked for the protection and conservation of global common goods. In this special report, the WBGU makes recommendations for a politically viable implementation of the concept of global user charges for three specific areas of application: