In the near future, Uninhabited Aircraft Systems (UAS) will bring significant benefits to a rapidly growing number of operations beyond defence. In civilian applications, UAS have the potential to be used for airborne mineral explorations, crop-yield monitoring, traffic monitoring in transportation systems, digital mapping, inspection of power-grid lines, and data collection for environmental and climate research. Due to this potential, nations worldwide are seeking to develop further their UAS capabilities. Over the past ten years, research activities in industry and academia have been growing, and companies are designing and developing the next generation of UAS. As the level of autonomy in UAS operations increases, UAS must be able to either continue operating in the presence of faults and anomalous conditions, or shut down safely - this characteristic is described as robust autonomy. This book focuses on how robust autonomy in UAS can be quantified so national airworthiness authorities can certify UAS for operations￼ in the national airspace system.