The article discusses the role of EPA's Air and Energy Engineering Research Laboratory (AEERL) in pollution prevention research for cleaner air. For more than 20 years, AEERL has been conducting research to identify control approaches for the pollutants and sources which contribute to air quality problems. The Laboratory has successfully developed and demonstrated cost-effective sulfur dioxide, nitrogen oxides, and particulate control technologies for fossil fuel combustion sources. More recently, it has expanded its research activities to include indoor air quality, radon, organic control, stratospheric ozone depletion, and global warming. AEERL also develops inventories of air emissions of many types. Over the last several years, it has made substantial efforts to expand research on pollution prevention as the preferred choice for air emissions reduction.