Obesity and overweight pose significant challenges to the armed forces in the United States, affecting service members (including active duty, guard, and reserve components), veterans, retirees, and their families and communities. The consequences of obesity and overweight in the armed forces influence various aspects of its operations that are critical to national security.On May 7, 2018, the National Academies of Sciences, Engineering, and Medicine, held a workshop titled "Understanding and Overcoming the Challenge of Obesity and Overweight in the Armed Forces." Speakers examined how obesity and overweight are measured in the armed forces and how they affect recruitment, retention, resilience, and readiness; discussed service-specific issues related to these problems and highlighted innovative strategies to address them through improved nutrition, physical activity, and stress management; and offered perspectives from outside of the armed forces on approaches to prevent and treat obesity. They also discussed the challenges and opportunities related to overcoming the concerns posed by obesity and overweight in the armed forces, military families, and their communities, including potential cross-sector opportunities. This publication summarizes the presentations and discussions from the workshop.