The international character of today's most pressing environmental problems has become a key challenge for environmental policy making. As regulation by a supranational authority is not a realistic option at present, policymakers have to rely on decentralized approaches to the management of international environmental resources.This study combines two core dimensions of international environmental policy: the traditional search for cost-effective policy instruments and the creation of incentives for voluntary cooperation among sovereign nations. The analysis offers some clear-cut policy recommendations for the design of environmental treaties and for the further development of existing international institutions to protect the global environment.