This book provides an in-depth study of high-voltage direct current (HVDC) systems and flexible AC transmission systems (FACTS), highlighting their applications in modern electric power networks. It covers the principles, design, operation, and control of these technologies, which are crucial for improving transmission efficiency, stability, and reliability. The text explores both theoretical foundations and practical implementations, including power flow management, voltage regulation, and integration of renewable energy sources. Readers gain insights into system optimization, fault management, and technological advancements that enable more flexible and sustainable electricity transmission. Designed for students, engineers, and researchers, the book offers a comprehensive understanding of advanced power system technologies, providing the tools to analyze, design, and implement HVDC and FACTS solutions in contemporary electric networks.