There has been an increase in the use of tradeable permit systems as a cost-effective environmental policy measure in OECD countries in recent years. For example, several countries are now implementing carbon trading schemes in the light of the Kyoto Protocol, and an EU-wide system will come into force in 2005. This publication brings together reports presented at an OECD workshop, held in 2003, to discuss key issues in the evaluation of the environmental effectiveness and economic efficiency of such systems. Areas covered include: successful design features; their application in a variety of different contexts such as air pollution controls, the degradation of wetlands, agricultural pollution, water scarcity and fisheries depletion; and technical issues; as well as case studies from Australia, the Netherlands, New Zealand and the United States.