Optimal-Peak-Sidelobe Polyphase Code is an in-depth guide to efficiently designing optimal-peak-sidelobe polyphase codes. The search for low-sidelobe polyphase codes has challenged researchers since World War II, but the exponential computational complexity of the problem ensures that new insights and algorithms continue to emerge. This resource provides working algorithms and computer code to find ways to build optimal peak sidelobe polyphase codes and code sets. The goal of this book is to narrow the focus to optimal polyphase codes, so as to give a practical limit to the topic, and then to provide readers with the most valuable insights and most efficient algorithms available. Given the demanding timelines of radar and communication system development, this book serves as a practical guide to implementing efficient search methods without starting from scratch. Readers will encounter intriguing connections to Algebraic Group Theory, Combinatorics, and advanced mathematical techniques that drive efficiency in code search and optimization. Whether developing cutting-edge radar waveforms or refining signal processing techniques, this book delivers the tools and knowledge needed to push the boundaries of performance and efficiency. Beyond radar waveform design, the principles explored in this book hold significant relevance for professionals in communications, radio astronomy, and laser optics, where signal integrity and sidelobe suppression are critical. includes combinatorics, quantum sensing, cognitive architectures, and interference mitigation in sensor systems. Greg Coxson has been teaching electrical engineering courses and developing a course in Principles of Radar at the United States Naval Academy (USNA) in Annapolis Maryland. Prior to joining USNA, he worked as a radar systems engineer at Hughes Radar in El Segundo, California, Lockheed Martin MS2 in Moorestown, New Jersey, Technology Service Corporation in Silver Spring, Maryland, and the Radar Division at the Naval Research Laboratories (NRL) in Washington DC. Jon Russo completed Bachelor's and Master's degrees in electrical engineering at Cornell University, where he was a teaching assistant and helped with the summer college program. In 1992 he joined the research group at Lockheed Martin Advanced Technology Laboratories working in communications, radar, hardware design, reconfigurable computing, cognitive radio, and quantum sensing.