The design of complex control systems often poses problems best captured by means of discrete event system models, such as state machines. Indeed, many complex control systems behave, at a suitable level of abstraction, like collections of interacting, asynchronous, event-driven subsystems. Over the last couple of decades, control scientists have therefore worked at developing comprehensive theories of the control of discrete event systems. One leading approach is supervisory control, founded by Ramadge and Wonham.