There is no integrated regime governing efforts to limit the extent of climate change. Instead, there is a regime complex: a loosely-coupled set of specific regimes. We describe the regime complex for climate change and seek to explain it, using interest-based, functional, and organizational arguments. This institutional form is likely to persist; efforts to build a comprehensive regime are unlikely to succeed, but experiments abound with narrower institutions focused on particular aspects of the climate change problem. Building on this analysis, we argue that a climate change regime complex, if it meets specified criteria, has advantages over any politically feasible comprehensive regime. Adaptability and flexibility are particularly important in a setting—such as climate change policy—in which the most demanding international commitments are interdependent yet governments vary widely in their interest and ability to implement them. Yet in view of the serious political constraints, both domestic and international, there is little reason for optimism that the climate regime complex that is emerging will lead to reductions in emissions rapid enough to meet widely discussed goals, such as stopping global warming at two degrees above pre-industrial levels.