Proponents of agricultural biotechnology believe that genetically modified (GM) crops have the potential to provide great ecological benefits, such as reduced pesticide and land use, as well as agricultural benefits. However, given the rapid emergence of commercial GM crops and the likely increase in their use, many groups have raised concerns about the potential unintended, adverse ecological effects of these crops. Some ecological concerns are enhanced development of pest resistance, crosspollination with wild relatives, and reductions in beneficial insects or birds. Ecological Monitoring of Genetically Modified Crops considers the latest in monitoring methods and technologies and to asks--What are the challenges associated with monitoring for ecological effects of GM crops? Is ongoing ecological monitoring of GM crops a useful and informative activity? If so, how should scientifically rigorous monitoring be carried out in the variety of ecological settings in which GM crops are grown?