This report responds to the October 25, 2018, Presidential Memorandum on Developing a Sustainable Spectrum Strategy for America’s Future and contains recommendations for prioritizing R&D to advance radio frequency spectrum access and efficiency, as called for in Section 2(c) of the Memorandum. The report focuses on R&D efforts to create a flexible R&D environment that advances spectrum technologies to meet current and future spectrum requirements for the broad communications needs of the Nation. This report supports Administration spectrum goals by identifying spectrum R&D priorities across Federal and private sectors for ongoing, increased, and new R&D investments in both the near term (5-10 years) and the long term (greater than 10 years). The priorities report looks beyond only mobile and broadband communications to examine the entire spectrum ecosystem, including science and meteorological observations, radar, radiolocation, and navigation. The report considers the impact of R&D across the electromagnetic spectrum, as well as emerging network architectures and application domains expected in the future that will rely on the existence of a reliable wireless communication system.