Indoor Air Quality deals with the content of interior air that could affect the health and comfort of building occupants. IAQ may be compromised by microbial contaminants (mold, bacteria), chemicals (carbon monoxide, radon, allergens) or any mass or energy stressor that can induce negative health effects. Recent findings have demonstrated that indoor air is often more polluted than outdoor air (albeit with different pollutants), although this has not changed the common understanding of air pollution. In fact, indoor air is often a greater health hazard than the corresponding outdoor setting. Using ventilation to dilute contaminants, filtration, and source control are the primary methods for improving indoor air quality in most buildings.

In the last several years, a growing body of scientific evidence has indicated that the air within homes and other buildings can be more seriously polluted than the outdoor air in even the largest and most industrialized cities. Other research indicates that people spend approximately 90 percent (90%) of their time indoors. Thus, for many people, the risks to health may be greater due to exposure to indoor air pollution than outdoors.