Control of air or pure oxygen dissolution in the mixed liquor is an important parameter in the activated sludge process. Increasingly, there is an economic incentive to minimize excess oxygenation. The hypothesis is that a desirable automatic control strategy is to add only sufficient air or oxygen to meet the time-varying oxygen demand of the mixed liquor. Field tests indicate that the benefits of such a control strategy are improved process performance and efficiency. This paper summarizes information presented in a design manual entitled “Design Procedures for Dissolved Oxygen Control of Activated Sludge Processes” prepared for the U.S. Environmental Protection Agency (EPA) (to be published).