This textbook provides fundamental theory and application of satellite communications and networks in a format suitable for university students and professionals working in the field. The book first outlines the types of satellites and their uses, then goes on to cover satellite orbits and constellation design; satellite system architecture; air interface and physical layer; and integrated satellite-terrestrial networks. A thorough discussion on 5G and 6G non-terrestrial networking (NTN) is included. The book shows how and why satellites are playing a key role in supporting critical infrastructures of society, such as energy and telecommunication networks and different forms of traffic on roads, sea and in the air. The book also discusses threats to satellites and how cybersecurity plays a role. The book features end-of-chapter questions and exercises, homework problems including mathematical exercises and practice questions, PowerPoint slides, and a solution manual. The book is ideal for upper undergraduate and graduate students in telecommunications curriculum.