Land quality and land degradation affect agricultural productivity, but quantifying these relationships has been difficult. Data are limited, and impacts are sensitive to the choices that farmers make. Summarizing new research by economists, soil scientists, and geographers, this report explores the extent to which land quality and land degradation affect agricultural productivity, how farmers' responses to land degradation are influenced by economic, environmental, and institutional factors, and whether land degradation poses a threat to productivity growth and food security. Results suggest that land degradation does not threaten food security at the global scale, but does pose problems in areas where soils are fragile, property rights are insecure, and farmers have limited access to information and markets.