Chemical use in agriculture has, over the last fifty years, been the good, the bad, and the uncertain. By all accounts, agricultural productivity increased significantly in the last half century due in part to the introduction and expanded use of agricultural chemicals. More recently, however, some agricultural practices, including increased chemical use, are viewed as having a major impact on the larger ecosystem and as being an important source of environmental nonpoint pollution. Recent groundwater-monitoring programs in the United States sponsored by the U.S. Environmental Protection Agency (EPA) have revealed contamination of underground water supplies by pesticides, nitrates, and other industrial organic chemicals. It has also been questioned whether the high rates of productivity growth that have characterized modern agriculture can be sustained with technologies that disrupt the ecosystem. While there is no doubt that production agriculture does affect the ecosystem, it is not obvious that these effects are necessarily widespread and deleterious to the environment or to long-run productivity, or, if they are, how they should be valued and traded-off with other social objectives.