The environmental legacy of nuclear weapons research, production of nuclear materials, and testing is one of the United States government’s largest financial liabilities. For decades, these activities produced large volumes of radioactive and hazardous waste and considerable environmental contamination. Over the past two decades, many of the facilities, which were once vital to our national defense, have become excess. Recognizing the changing missions at many former Department of Energy sites, a new organization, Environmental Management, was created in 1989 with the primary mission of site clean-up or environmental restoration, including the necessary management of waste and surplus nuclear material and application of science and technology to the tasks at hand. The Environmental Management program brought a needed mission focus to our unprecedented stewardship responsibility to clean-up these sites, deactivate facilities, and manage remaining inventories of U.S. government-owned spent nuclear fuel, radioactive and hazardous waste, and surplus nuclear materials.