Environmental regulation is evolving and will require billions of dollars in investments to improve the operation of wastewater systems and to control the wet-weather pollution. The optimization of existing facilities before building new ones has been emphasized as a preferred strategy and, consequently, municipalities are learning that they can avoid costly and unnecessary capital improvement projects. Real-time control is a technology that serves to optimize the operation of wastewater systems. However, it is still not widely used, although it is gaining acceptance in the municipal engineering community. More and more municipalities are evaluating the potential of real-time control for their systems. Nevertheless, there are relatively few examples of actual real-time control applications or publications on this topic. Many issues still need to be addressed, ranging from the evaluation of real-time control to its implementation. Some of the criteria that favour the implementation of real-time control systems are presented, including safety, reliability, adaptability and flexibility, and such a presentation is complemented by case studies of operational real-time control systems illustrating these characteristics.