The modern era of global environmental politics coincided with contemporary scholarship on transnational actors. The 1972 United Nations Conference on the Human Environment took place in Stockholm one year after a special issue of International Organization was released entitled “Transnational Relations and World Politics” (Nye and Keohane 1971). Since then, there has been a dramatic growth both in the involvement of transnational actors in environmental politics and research on their activities. The growing presence of transnational actors has been evident at the principal global environmental conferences. At the Stockholm Conference in 1972 some 170 nongovernmental organizations were present, in 1992 around 1,400 were registered at the Rio Earth Summit, 8,000 at the World Summit on Sustainable Development in Johannesburg in 2002, and 9,856 at the Rio+20 Summit held in 2012. Indeed, it is estimated that transnational organizations generally had grown from 2,795 in 1970 to 48,220 by 2010 (Andonova 2011).