The paper describes (1) major provisions of Title III of the 1990 Clean Air Act Amendments (CAAAs) which formally established a new regulatory approach which would avoid past impediments and accelerate emission reductions, and (2) the research that the U.S. EPA has initiated to support state and federal regulatory officials as they implement the extensive new provisons of the CAAAs. Toxic emissions from stationary air pollution sources have been recognized as a national health problem for several decades. Unfortunately, a large percentage of these hazardous air pollutant (HAP) emissions have not been controlled because, between 1977 and 1990, the risk-based federal regulatory program to reduce them addressed only a few pollutants. Disputes between industry, the U.S. EPA, and environmental groups over health effects data, exposure levels, and what constitutes an ample margin of safety to protect the public health were the primary impediments to progress and limited the number of National Emission Standards for Hazardous Air Pollutants (NESHAPS) issued to only 10. The lack of progress toward reducing HAP emissions raised public concern and convinced Congress to design the modified approach.