The literature on the political economy of the global environment is a hybrid of political economy, international relations (IR), and international environmental politics, looking at the formal and informal institutional factors which give rise to unsustainable habits. The physical environment has long been the subject of social scientists, who recognized that patterns of social activity might contribute to environmental degradation. One of the most common formulations of environmental issues as a collective action is through the metaphor of the Tragedy of Commons, which argues that overpopulation worldwide would undoubtedly contribute to extensive resource depletion. Following the formulation of the core properties of environmental issues as lying at the interstices of a variety of human activities, implications followed for how to conduct research on international environmental politics and policy. Realist and neorealist traditions in international relations stress the seminal role of power and national leadership in addressing environmental problems. Neoliberal institutionalists look at the role of formal institutional properties in influencing states’ willingness to address transboundary and global environmental threats. On the other hand, the constructivist movement in international relations focuses on the role of new ecological doctrines in how states choose to address their environmental problems, and to act collectively. Ultimately, the major policy debates over the years have addressed the political economy of private investment in environmentally oriented activities, sustainable development doctrines, free trade and the environment, environmental security, and studies of compliance, implementation, and effectiveness.