This chapter investigates the role of formal international institutions in the broader process of international efforts to respond to and manage global and transboundary environmental risks. International institutions focus on institutional learning. The chapter takes an inductive approach to the study of institutions and social learning by studying a selective but illuminating set of vignettes of new directions pursued by international institutions and lessons learned within the institutions by their constituent members. National governments are the primary actors in the management of global environmental risks. The most responsive institutions in which learning occurred were the United Nations Environment Program (UNEP) and the Villach Group. The World Meteorological Organization (WMO) experienced some learning, but this was fairly delayed because of the rigid structures through which information to the institution flowed. The Intergovernmental Negotiating Committee (INC) and Intergovernmental Panel on Climate Change (IPCC) learned very little.