Process control is about making the process output behave in the desired way by manipulating the process input in an automatic way. Process controllers have contributed much to improving the quality of products and reducing utility consumption. In this part, the PID controller and the tuning methods are introduced in Chapters 4 and 5. The two chapters are extremely important to understanding the basic concepts of feedback process control and various real-world controllers implemented in industry. Chapter 6 introduces several important tools (Bode plot and Nyquist plot) and terms (characteristic equation, ultimate frequency and gain, gain margin and phase margin) to analyze/describe the closed-loop dynamic characteristics of the designed feedback controller. Enhanced control strategies using additional measurements and the process model, which have been widely used in industry, are discussed in Chapter 7.