The application of biotechnology to agricultural problems holds great promise and inspires lively debate. The promise of agricultural biotechnology includes crops that resist pests and diseases, thrive in spite of environmental stresses like drought or salinity, and provide increased nutritional value. The debate encompasses both biological and societal questions, many of which are not easily answered. This paper will discuss some of the more commonly cited environmental concerns associated with transgenic plants and animals. They are grouped into five categories: movement of transgenes, unintended effects, viral recombination, evolution of resistant pests, and whole organism characteristics. Since 1992, USDA has supported research to characterize and assess possible risks associated with the release of transgenic organisms into the environment. A goal of this research is to assist Federal regulatory agencies in making science-based decisions regarding biotechnology. A review of grants supported by USDA's Biotechnology Risk Assessment Research Grants Program shows how research to address environmental concerns has evolved over time.