In Chap. 5, we provided detailed discussions about the classical linear control systems or PID control systems with various design methods. One of the most important and critical key requirements to design and implement a PID control system is that the dynamic model of the process or plant is the prerequisite condition . However, in some actual applications, sometimes it is very difficult or impossible to obtain those models. Therefore, it looks like that it is impossible to design any appropriate controller for those control systems.