This book offers a comprehensive review of collision avoidance techniques and safe trajectory planning for manned and unmanned ships, together with extensive information on how to develop and implement algorithms for applications in real-world settings. It describes the most relevant decision-support systems and guidance systems used in the control of marine craft, giving a special emphasis to autonomous vehicles, but also covering manned ones. Thanks to its good balance of theory and practice, and the inclusion of basic explanations of all essential concepts, this book fills an important gap in the literature of marine navigation, providing not only researchers and practitioners with a timely reference guide to safe trajectory planning, but also supporting students and newcomers to the field.