Sociologist Robert Nisbet conjectured that “when the history of the twentieth century is finally written, the single most important social movement of the period will be judged to be environmentalism”; (1982, p. 10). This assessment has been reinforced by subsequent events. Environmental concern has risen to the top of political agendas in the United States and many other countries, becoming a major consideration in international relations. A major force for the globalization of environmental politics in the United States has been the growing international concern of nongovernmental environmental organizations (NGOs). Almost all of the larger environmental NGOs now have significant international programs that attempt to influence public policies. Transnational collaboration between governments and NGOs on environmental issues has become a characteristic of contemporary politics in North America and Western Europe. Global issues such as climate change, ozone depletion, transboundary air and water pollution, endangered species, and uses of outer space will henceforth give an international dimension to national environmental policies.