The architecture of global climate governance, constructed over the three decades from the Rio Earth Summit to the Glasgow Climate Pact, is fundamentally a story of international organizations. These entities—each with distinct mandates, powers, and constituencies—have been the primary architects, engineers, and custodians of the global response to the climate crisis. They have transformed a complex scientific phenomenon into a sustained subject of high politics, forged fragile agreements among sovereign states, and generated the knowledge necessary for action. This chapter examines the pivotal roles of four such organizations: the United Nations (UN), the Intergovernmental Panel on Climate Change (IPCC), the International Energy Agency (IEA), and the United Nations Environment Programme (UNEP).