This article is concerned with private environmental governance at the global level. It is widely acknowledged that private actors play an increasing role in global environmental politics. Corporations lobby states during negotiations on multilateral environmental agreements (MEAs), featuring prominently in the implementation of international accords. They also interact with each other, as well as with states and other nonstate actors, to create institutional arrangements that perform environmental governance functions. The rise of such private forms of global governance raises a number of questions for the study of global environmental politics: How does private governance interact with state-centric governance? In what ways are the roles/capacities of states and nonstate actors affected by private governance? Does the rise of private governance signify a shift in the ideological underpinnings of global environmental governance? This article explores these questions, seeking a better understanding of the significance of private environmental governance (PEG) for International Relations.