The future competitiveness of the United States in an increasingly interconnected global economy depends on the nation fostering a workforce with strong capabilities and skills in science, technology, engineering, and mathematics (STEM). STEM knowledge and skills enable both individual opportunity and national competitiveness, and the nation needs to develop ways of ensuring access to high-quality education and training experiences for all students at all levels and for all workers at all career stages. The National Science Foundation (NSF) holds a primary responsibility for overseeing the federal government's efforts to foster the creation of a STEM-capable workforce. As part of its efforts in this endeavor, NSF's Directorate on Education and Human Resources asked the National Academies of Sciences, Engineering, and Medicine to convene a workshop that would contribute to NSF's preparation of a theoretical and evidence-based STEM Workforce Development R&D Core Framework. Participants discussed research themes, identified gaps and emerging research opportunities, and recommended refinements in the goals of the framework. This report summarizes the presentations and discussions from the workshop. The following are appended: (1) Workshop Agenda; (2) Biographical Sketches of Workshop Speakers and Planning Committee Members; (3) Anonymous Participant Responses to the Pre-summit Question; and (4) List of Workshop Registrants.