The strength of PID control lies in its simplicity, lucid meaning, and clear effect. Although PID control is a widely accepted method for controlling mechanical systems it is hard to find a book on PID control for mechanical systems. This monograph discusses thoroughly the theoretical bases, e.g., optimality of PID control, performance tuning rules, automatic performance tuning method, and output feedback PID control for mechanical control systems - clearly presenting the characteristics and theory of mechanical control systems.