In-situ air sparging (IAS) is a rapidly emerging remediation technology for treatment of contaminants in saturated zone soils and groundwater. Injection below the water table of air, pure oxygen, or other gases may result in removal of contaminants by volatilization or bioremediation. Less commonly, IAS can be used to immobilize contaminants through chemical changes such as precipitation. This Engineer Manual (EM) provides guidance for evaluation of the feasibility and applicability of IAS for remediation of contaminated groundwater and soil and, as a secondary objective, describes design and operational considerations for IAS systems.