Hazardous particles or dusts, for purposes of the paper, are considered to be those whose size or chemical species cause harm to the population through deposition in the lungs and other portions of the pulmonary tract. A small number of pollutants, some of which are particles, have been designated under the program from the Clean Air Act for National Emission Standards for Hazardous Air Pollutants (NESHAP); a larger number are being considered for NESHAP. Several R&D needs are listed including: sensing of excess emission of hazardous dust from control equipment; need to retrofit for improved capture of small particles; improved collection of fine condensable aerosols; and modeling of control technology for hazardous particles. Indoor air particles and dusts are discussed with emphasis on characterization, indoor air cleaners, and asbestos in residences. Radon in the indoor environment is discussed as an emerging problem. Finally, an indoor air/radon model is discussed linking indoor air dusts to lung deposition.