The debate on institutional reform of international environmental policy-making has gained momentum. This article discusses whether the United Nations Environment Programme (UNEP) should be replaced with a stronger world environment organization. First, it outlines different models of a world environment organization. It argues that the best option for the next decade would be to upgrade UNEP to a full-fledged international organization while maintaining the current system of decentralized, issue-specific international environmental regimes. In the long run, however, a world environment organization should lead to a closer integration and coordination of the myriad environmental treaties in the same manner in which the World Trade Organization has integrated the major trade agreements. Second, the article comments on the writings of both advocates and opponents of a world environment organization, with a focus on the contributions to this inaugural issue of Global Environmental Politics.