The widespread proliferation of Unmanned Aerial Systems (UAS) among both state and non-state actors is cause for concern to U.S. Operational Commanders. No longer does the U.S. have a monopoly on UAS operations. Nearly 90 countries now operate some type of UAS capability and, with increasingly affordable and available technology, that trend is increasing at an alarming rate. This paper evaluates the current and anticipated future threat posed by adversary UAS to U.S. forces, both in the form of system capabilities and methods of employment. It also addresses present counter UAS capabilities and recommends ways and means to provide better operational protection. Throughout the paper, the term UAS encompasses all types of unmanned aircraft and is used synonymously with the terms Unmanned Aerial Vehicle (UAV), Remotely Piloted Aircraft (RPA), and drone.