Graduate medical education (GME) is critical to the career development of individual physicians, to the functioning of many teaching institutions, and to the production of our physician workforce. However, recent reports have called for substantial reform of GME. The current lack of established GME outcome measures limits our ability to assess the impact of individual graduates, the performance of residency programs and teaching institutions, and the collective contribution of GME graduates to the physician workforce. To examine the opportunities and challenges in measuring and assessing GME outcomes, the National Academies of Sciences, Engineering, and Medicine held a workshop on October 10-11, 2017, in Washington, DC. Workshop participants discussed: meaningful and measurable outcomes of GME; possible metrics that could be used to track these GME outcomes; possible mechanisms for collecting, collating, analyzing, and reporting these data; and further work to accomplish this ambitious goal. This publication summarizes the presentations and discussions from the workshop. [Payal Martin, Mariana Zindel, and Sharyl Nass served as Rapporteurs. Numerous organizations sponsored this work and the full list can be seen in the document.]