Tropical deforestation, the cause of 20% of greenhouse-gas emissions, is recognized as a critical element of climate change. However, reducing emissions from deforestation, although providing important co-benefits such as biodiversity conservation, is a complicated policy problem. This symposium will bring together speakers from both the scientific and policy communities working on this issue to examine how technical advances can make it possible to reach international agreement. At the same time, it highlights debates about some of the most contentious issues, such as the role of markets and the respective roles of industrialized and tropical nations, that stem from fundamental political disagreements. The participants exemplify a wide range of contrasting positions on both the scientific and political sides of the issues.