Safety is the top priority of the Federal Aviation Administration (FAA) as it manages America's National Airspace System (NAS). The NAS is the common network of U.S. airspace - air navigation facilities, equipment, and services; airports or landing areas; aeronautical charts, information and services; rules, regulations, and procedures; technical information; and manpower and material. Thanks to the expertise of people and the support of technology, tens of thousands of aircraft are guided safely and expeditiously every day through the NAS to their destinations. Air traffic controller workload and traffic volume are dynamic, and so are the FAA's staffing needs. A primary factor affecting controller workload is the demand created by air traffic, encompassing both commercial and non-commercial activity. Commercial activity includes air carrier and commuter/air taxi traffic. Non-commercial activity includes general aviation and military traffic. Since the early 1990s, unmanned aircraft systems (UAS) have operated on a limited basis in the National Airspace System (NAS) and mainly supported public operations, such as military and border security operations. In recent years, UAS and operations have significantly increased in number, technical complexity, and application. The list of uses has rapidly expanded to encompass a broad range of activities, including aerial photography, surveying, communications and broadcast, as well as hobby and recreation. In December 2015, the FAA began registration of all Unmanned Aircraft Systems (UAS). As policy and technology updates allow widespread use of UAS for commercial applications, impact on Air Traffic Control workload will be incorporated into our models and forecasts. Oversight of UAS is aided by FAA's new compliance philosophy which is designed to help identify and correct potential hazards before they result in an incident or accident. Adequate numbers of controllers must be available to cover the peaks in traffic caused by weather and daily, weekly or seasonal variations, so we continue to "staff to traffic." This practice gives us the flexibility throughout each day to match the number of controllers at each facility with traffic volume and workload.