Efforts to mitigate climate change have focused on reducing carbon dioxide (CO2) emissions into the atmosphere. Some of these efforts center on reducing CO2 emissions from deforestation, since deforestation releases about 17% of all annual anthropogenic greenhouse gas (GHG) emissions and is seen as a relatively low-cost target for emissions reduction. Policies aimed at reducing deforestation are central points of a strategy to decrease carbon emissions, reflected in pending legislation in Congress (e.g., H.R. 2454 and S. 1733) as well as in international discussions, such as the December 2009 negotiations in Copenhagen. Forests exist at many latitudes. Many are concerned about the possible impacts of losing boreal and temperate forests, but existing data show little, if any, net deforestation, and their loss has relatively modest carbon consequences. In contrast, tropical deforestation is substantial and continuing, and releases large amounts of CO2, because of the carbon stored in the vegetation and released when tropical forests are cut down. There are many causes of tropical deforestation-commercial logging, large-scale agriculture (e.g., cattle ranching, soybean production, oil palm plantations), small-scale permanent or shifting (slash-and-burn) agriculture, fuelwood removal, and more. Often, these causes combine to exacerbate deforestation; for example, commercial logging often includes road construction, which in turn opens the forest for subsistence farmers. At times, tropical deforestation results from weak land tenure and/or weak or corrupt governance to protect the forests. Congress and international bodies are discussing various policies to reduce carbon emissions from deforestation and forest degradation (REDD). Reducing deforestation in the tropics is likely to have additional benefits as well, such as preserving biological diversity and sustaining livelihoods for the rural poor and for indigenous communities and cultures. Proposals may be adapted to address local and regional causes of deforestation. Various forestry practices can reduce the impacts of deforestation, and several market approaches are evolving to compensate landowners for preserving their forests. Many challenges remain for implementing REDD programs, particularly internationally, including monitoring REDD projects and improving developing-country capacity to ensure compliance. Existing evidence on forests and deforestation suggest the difficulties might be significant. Measuring forests is complicated, with multiple definitions, inaccessible sites, and expensive, complicated, and imperfect measurement technologies. This report provides basic information on forests and climate change. The first section discusses the linkages between forests and climate. The next three describe the characteristics of the three major forest biomes, with an overview of deforestation causes and impacts. This is followed by an overview of approaches to reducing deforestation. The final section examines issues related to forest and deforestation data.