This chapter examines the main characteristics and components of Indoor Environmental Quality (IEQ) and the principal causes of indoor pollution. It also examines the factors that impact Symptoms of Sick Building Syndrome and Building-Related Illness as well as the measures that can be taken to prevent them. Also, scrutinized are the main causes of indoor pollution and their impact on IEQ. Also analyzed are American society of Heating, Refrigerating, and Air-Conditioning Engineers established procedures for determining minimum acceptable ventilation rates and health hazards (such as radon, asbestos, lead, carbon dioxide, formaldehyde, etc.). Organic Contaminants Pesticides, Biological Contaminants (mold, fungus, bacteria, viruses, etc.) and their impact on IEQ are also examined. Toward the end of the Chapter recommended illumination levels, daylighting strategies, ventilation systems and, finally (IEQ), best practices are looked at.