The US military currently conducts the most flights of unmanned aircraft systems (UAS) worldwide, including intelligence, surveillance, reconnaissance, and combat missions in current theaters of war, and training flights in the US National Airspace System (NAS). Other militaries, particularly the Israel Defense Force, also regularly conduct UAS missions. Aviation regulations were developed for manned aircraft operations; UAS‐specific regulations have yet to appear. The aviation regulations set the requirements for UAS operations in unrestricted airspace, with requirements for a special experimental certificate for civil (commercial) operations, or a certificate of authorization or waiver (COA) for public (government) operations that include domestic military, government agencies, law enforcement, emergency first‐responders, and public universities. This chapter describes the range of UAS operated today, in terms of the physical characteristics and performance that must be taken into account for flight tests and operations. Examples are selected from UAS operating in the NAS. The airspace regulatory environment is discussed with an overview of COA application process and procedures for deploying and small UAS in the NAS are described for closed range testing and nomadic, science‐based missions. Finally, the state of the public perception of UAS operations is discussed.