Jan. 31 – Feb. 3, 1999, in Bethesda, Maryland, the workshop on Ecological Effects of Pest Resistance Genes in Managed Ecosystems was organized to promote multidisciplinary discussions that would lead to a synthesis of what we already know, and what we don’t know, regarding the environmental impact of pest resistant crops. In so doing, the workshop provided an opportunity to reexamine a key issue related to the responsible development and use of agricultural biotechnology products. The workshop focused on seven groups of crop species that have weedy relatives in North America: berries, certain grains and grasses, poplar, sunflower, squash, and Brassica species.