Source control is a desirable approach to both preventing and mitigating indoor air quality (IAQ) problems as it is often technically more difficult to control contaminants once they are airborne than to prevent their generation or release in the first place. Though source control can be described as a mitigation measure in a generic sense, it is in most instances case specific. Its application depends both on the contaminants and their sources. Source control of chemical contaminants can be achieved at two levels: avoidance of known significant sources in designing and equipping buildings and implementation of remedial measures once an IAQ manifests itself. The avoidance/prevention approach requires characterization of emissions from sources so that choices can be made relative to product selection. Source control comprises a variety of principles and applications based on the nature of individual contaminants and contamination problems.