Climate change is now a mainstream part of the international political agenda. Indeed, for anyone interested in, and concerned about, international affairs, few issues are more important. Climate change is not solely a technical issue to be resolved by scientists, but a political issue with political implications at all levels of global governance. Consequently, climate change has been the subject of three decades of diplomacy, and it is now a major concern of governments, international organizations, businesses and nongovernmental organizations, as well as increasing numbers of people around the world. But as the problem has grown in prominence, so have predictions of its adverse impacts, many of which are being felt today. Political responses have dramatically failed to keep up with the accelerating pace of climate change. Given the need to act very aggressively to limit and cope with climate change and its effects, a question arises: Why has more not been done? The purpose of this collection of essays is to help answer that question by revealing and applying some of the latest thinking about climate change in international affairs, and to explore how various proposals for tackling it will affect interstate relations in coming years. In this introduction I set the stage for the essays to follow by (1) recounting recent assessments of how climate change affects the world and (2) summarizing the history of interstate responses to those assessments.