This book presents the latest international research achievements in complex chaotic systems, establishing itself as an reference with high value in nonlinear dynamics and chaos theory. The book systematically explores dynamical behaviors of complex chaotic systems through control methods and engineering technologies, with particular emphasis on chaos synchronization and its revolutionary applications in secure communication. It introduces chaos synchronization including anti-synchronization, projective synchronization, hybrid projective synchronization, and various advanced synchronization techniques for both integer-order and fractional-order complex chaotic systems. Furthermore, the work demonstrates pioneering applications of chaotic systems and synchronization technologies in the field of secure communication. This publication stands out through its comprehensive pedagogical features, which include detailed mathematical frameworks and illustrative case studies. The content is strategically organized to guide readers progressively from fundamental concepts in Chapter 1, through various synchronization types of integer-order systems in Chapters 2-12, followed by in-depth analysis of fractional-order systems in Chapters 13-18, and culminating with practical encryption applications in the final chapters. The principal merit of this work resides in its distinctive integration of theoretical rigor and practical applicability, providing readers with both foundational comprehension and executable methodologies for complex system analysis. It serves not only as an essential reference resource for secure communication but also establishes a solid theoretical foundation and offers innovative methodological pathways for researchers exploring complex systems.