Although the general theory of global warming has been a part of scientific research and debate since the end of the nineteenth century, an international legal regime to address the problem of climate change began to develop only in the late 1980s. This book chapter provides an historical and legal introduction to the evolution of the United Nations climate change regime reviewing the development of the regime from its emergence through to the adoption of the major global climate agreements. The chapter outlines the principal elements of the legal regime and concludes with some brief observations about the future direction of the UN climate change regime. The chapter notes that the regime has, so far, aimed at the widest participation possible, although this has been undermined by the United States withdrawal from the Kyoto Protocol in 2001 and the reluctance of some developing countries to limit their greenhouse gas emissions.