The Flexible Alternative Current Transmission System and Distribution Flexible AC Transmission System (FACTS/DFACTS) are a new converging technology based on the Power Electronics, Control Theory and Power System for revolution of ever more efficient control and better utilization of power and energy in the existing systems. The FACTS offers an opportunity to enhance controllability, stability and power transfer capability of AC transmission systems with fastest control speed. DFACTS is the extended modern technique of FACTS to focus on the Custom issues or power line conditioning in the distribution site as well as the Information Technology's Electricity Issues. During the last decade, a number of control devices under the term FACTS/DFACTS technology have been proposed and implemented. This course provides a comprehensive guide to FACTS, covering all the major aspects in research and development of FACTS technologies. Various applications are also included to demonstrate the issues and benefits of applying FACTS. This course involved in the operation and control of modern power systems by FACTS technology.