Most controls used in the activated sludge process are also important for biological nutrient removal (BNR) processes since activated sludge is typically an integral part of these processes. What distinguishes the BNR process is the need to ensure the proper source of energy and the proper means of respiration for the pollutant removal we want to accomplish. Activated sludge is intended to oxidize organic compounds in an aerobic environment. Depending on the specific treatment objectives, BNR processes may oxidize organic and inorganic compounds that require aerobic, anoxic, and anaerobic environments. This paper discusses the importance of maintaining the right source of energy and the right means of respiration in BNR systems, as well as other process control considerations that are needed to accomplish specific treatment objectives.