As described in the Chapter 1, indoor air quality (IAQ) problems arise when there is an inadequate quantity of ventilation air being provided for the amount of air contaminants present in a given space. Therefore, standards or guidelines attempting to regulate IAQ can do so by specifying minimum quantities of ventilation air, by specifying maximum concentrations of air contaminants that are allowable, or by specifying both. Therefore, this chapter is divided into discussions of both approaches. With respect to ventilation requirements, however, there is first a discussion of the various terms that are used for expressing the quantity of ventilation being provided. This is followed by a discussion of the actual guidelines and standards that exist that pertain to IAQ in nonindustrial buildings, both from the ventilation and contaminant approaches.