Economic globalization creates transboundary and global environmental externalities. A system of multilateral international environmental governance has evolved over the last 25 years as the international community has attempted to address the ecological externalities of economic globalization. Most observers of the 1972 United Nations Conference on the Human Environment (UNCHE), when the international community first acknowledged the urgency of dealing with global environmental threats, were skeptical that effective governance could be established for such issues. Yet governments are now held accountable to new standards of environmental behavior by carriers of values who had no standing in 1945. Not only has a stable set of expectations about reciprocal state practice been established, its form has evolved over time to become more comprehensive, reflecting growing scientific understanding about the behavior of ecosystems and the sensitivity of human societies to such dynamics. The norms, rules and strategies for environmental governance are no longer widely contested (Kratochwil and Ruggie 1986; Haas 1992; Crawford and Ostrom 1995).2 They are now enforced within a multilateral governance structure which systematically limits the role of the state. While states remain the putative sources of authoritative choice, officials are aware of two novel features of international environmental governance: that science is essential for the understanding of global environmental problems, thus shifting the determination of the scope of allocative decisions to the international institutions for science; and that states are increasingly accountable to domestic and transnational constituencies, thus shifting the locus of enforcement from states toward international institutions and NGOs.