Originally adopted in military networks as a means of ensuring secure communication when confronted with the threats of jamming and interception, spread-spectrum systems are now the core of commercial applications such as mobile cellular and satellite communication. This book provides a concise but lucid explanation and derivation of the fundamentals of spread-spectrum communication systems. The level of presentation is suitable for graduate students with a prior graduate-level course in digital communication and for practicing engineers with a solid background in the theory of digital communication. As the title indicates, the author focuses on principles rather than specific current or planned systems. Although the exposition emphasizes theoretical principles, the choice of specific topics is tempered by their practical significance and interest to both researchers and system designers. Throughout the book, learning is facilitated by many new or streamlined derivations of the classical theory. Problems at the end of each chapter are intended to assist readers in consolidating their knowledge and to provide practice in analytical techniques. Principles of Spread-Spectrum Communication Systems is largely self-contained mathematically because of the four appendices, which give detailed derivations of mathematical results used in the main text.