Fatigue has been on the National Transportation Safety Board (NTSB) Most Wanted List since the initial list in 1990 and remains a topic of active investigation to this day. The focus of this document was placed on Air Traffic Controller fatigue. In order to provide a starting point for future applied research pertaining to air traffic controllers, MITRE analyzed existing research to: 1) review what is known about the effect of fatigue on performance, 2) identify gaps in knowledge, and 3) develop a plan to fill those gaps. While a wealth of historical and current studies were examined during the course of the review, the majority of research fails to adequately address many current areas of concern within the aviation community. Gaps identified during the review were prioritized based on the estimated risk to safety in the National Airspace System (NAS) from highest to lowest. Finally, studies were recommended to quantify Air Traffic Controller fatigue for all positions, validate measures of Air Traffic Controller performance sensitive to fatigue, validate individual shift schedules, collect data to support sleep disorder policy, and validate human performance models to predict fatigue. Multiple appendices supporting the analysis are provided, forming a comprehensive collection of reference material for the global fatigue research community. A major contribution of this initiative is to help highlight the areas of research that are currently lacking and to encourage a collaborative effort to achieve a broader understanding of the causal factors for fatigue in aviation as well as investigate how these factors interact.