The article discusses air pollution engineering research at the U.S. EPA, and particularly AEERL's role in that research. The research programs are shifting from an initial focus on sulfur dioxide and nitrogen oxide pollution control to more complex and more difficult problems such as indoor air quality, air toxics, global climate change, and stratospheric ozone depletion. EPA research engineers are working closely with other researchers in both the private sector and other federal research organizations to identify, evaluate, and develop cost-effective engineering solutions. The AEERL works closely with the EPA regulatory and regional offices to ensure that the best engineering information is utilized to formulate and implement the Agency's environmental protection program.