This book focuses on security science and technology, data and information security, and mobile and network security for space-air-ground integrated networks (SAGINs). SAGIN are expected to play an increasingly important role in providing real-time, flexible, and integrated communication and data transmission services in an efficient manner. Today, SAGINs have been widely developed for a range of applications in navigation, environmental monitoring, traffic management, counter-terrorism, etc. However, security becomes a major concern, since the satellites, spacecrafts, and aircrafts are susceptible to a variety of traditional/specific network-based attacks, including eavesdropping, session hijacking, and illegal access. In this book, we review the theoretical foundations of SAGIN security. We also address a range of related security threats and provide cutting-edge solutions in the aspect of ground network security, airborne network security, space network security, and provide future trends in SAGIN security. The book goes from an introduction to the topic's background, to a description of the basic theory, and then to cutting-edge technologies, making it suitable for readers at all levels including professional researchers and beginners. To gain the most from the book, readers should have taken prior courses in information theory, cryptography, network security, etc.