The National Academies Roundtable on Obesity Solutions hosted a workshop in April 2023 exploring the current science on measures of body composition and body fat distribution with a focus on the strengths and limitations of body mass index (BMI) as a measure of adiposity and health. This workshop was the first part of a two-part series, Exploring the Science on Measures of Body Composition, Body Fat Distribution, and Obesity. Presentations addressed how BMI is perceived and used globally across different sectors, ethnic groups, cultures, and across the lifespan. The presentations explored the utility of BMI as a measure to assess obesity morbidity and mortality, as well as alternative measures to BMI, and their effects on obesity prevention, treatment, and policy. This Proceedings of a Workshop-in Brief summarizes the discussions held during the workshop.