This Article discusses the U.S. Environmental Protection Agency’s program to control fine particulate emissions 2.5 microns or smaller (PM2.5) in areas that fail to meet the national ambient air quality standards. The Article covers the sources and health effects of both direct emissions of particulate matter and secondary emissions that are transformed into PM2.5 in the atmosphere. Also discussed is the control of fine particulates from mobile, area, and major point sources; and the indirect control of PM2.5 through transportation planning and the program to reduce hazardous air pollutants. The Article concludes that controlling PM2.5 and its precursors from mobile sources by the federal government has been successful, but that control of these pollutants from area and point sources should be improved.