This book emphasizes the physical and engineering aspects of the power system frequency control design problem while providing a conceptual understanding of frequency regulation and application of robust control techniques. The material develops an appropriate intuition method relative to the robust load frequency regulation problem in real-world power systems, rather than describing mathematical analytical methods. The simplest possible frequency response models and control structures are used for conceptual explanations and practical control design. The book summarizes the author's long term research outcomes, contributions and experiences with power system frequency regulation during more than a decade of academic and working activities in Iran, Japan, and Australia.