As concern about indoor air quality (IAQ) has grown in recent years, understanding indoor aerosols has become increasingly important so that control techniques may be implemented to reduce damaging health effects and soiling problems. This paper begins with a brief look at the mechanics of deposition in the lungs and the aerosol dynamics that influence particles at all times. This discussion shows that the particle diameters must be known to predict dose or soiling and to determine efficient mitigation techniques. The particle sizes produced by the various indoor sources, as well as unusual aspects of each type of source, must be known so that this process may begin. This paper summarizes the results of a literature search into the sources, sizes and concentrations of indoor particles. There are several types of indoor particles: plant and animal bioaerosols and mineral, combustion and home/personal care aerosols. These types may be produced indoors or outdoors, entering through building openings. The sources may be short term, seasonal or continuous. Particle sizes produced vary from submicrometer to larger than 10-mu-m. The particles may be toxic or allergenic. This information is presented in a summary table and is discussed in the text.