The purpose of this study was to assess the Communications, Navigation, and Surveillance (CNS) capabilities needed to support future Air Traffic Management (ATM) functionality in the National Airspace System (NAS). The goal was to determine the most effective areas for research and technical development in the CNS field and to make sure the decision support tools under development match future CNS capabilities. The requirements for future ATM functions were derived from high level operational concepts designed to provide more freedom and flexibility in flight operations and from the Joint Research Project Descriptions (JRPDs) that are listed in the Integrated Plan for Air Traffic Management Research and Technology Development. This work was performed for the FAA/NASA Interagency Air Traffic Management Integrated Product Team.