Shewhart control charts are used extensively in manufacturing to statistically monitor product quality, a key element in the total quality management principles set forth by W. Edwards Deming. Activated sludge process control procedures developed by Alfred W. (Al) West do not take into account the variability in the process, which can be used to assess its state of statistical control. Shewhart control charts can be used to indicate when a process is tending out of control before it actually gets there, and when the process is in control and should be left alone. The theory and development of Shewhart control charts are presented. An investigation into the use of these charts in activated sludge process control was conducted at a full-scale facility. Three phases of testing are documented. The different testing phases reflect the evolution in the identification of the most appropriate performance variables and sample subgrouping strategy to be used to develop the control charts. Currently, a single settlometer test is performed four times a day that affords operationally defined measurements of the settling rate, extent of compaction, and degree of flocculation of the mixed liquor. The control charts well reflected process control changes and problems. The control charts can be used in making process control decisions and plant optimization.