Over the last ten years, the numbers of unmanned air vehicles (UAVs) or "drones" have changed from being just a few specialist systems, used for scientific data gathering and military purposes, to them proliferating in huge numbers. They are used across a broad range of different leisure, commercial and military activities. UAVs can be used for: movement of items in factories for manufacturing, passenger and freight transportation, can take various roles in the agriculture and forestry industries (dispensing seeds, watering and monitoring crops), remote sensing for the oil and gas industries, traffic flow monitoring, support of emergency services, hobbies, security, military and many other applications.The expansion in the use of unmanned air vehicles has come about due to the development of low cost, high performance stable platforms, employing equally low-cost communication and navigation systems supplemented by simple to use software and interfaces. Therefore, there is a need to be able to monitor the rapidly changing use of airspace, especially at low and normally neglected altitudes to ensure UAVs do not compromise safety or are used for malicious purposes. Radar is the only sensor able to perform this function on a 24-hour, all weather, wide-area basis.This book, concerned with radar surveillance of UAVs, has been compiled using contributions from the leading experts around the world to create a single body of knowledge on this important, yet still emerging, topic. It is aimed at advanced students and researchers with an interest in radar systems.