In April 2015, the Institute of Medicine convened a workshop to explore the potential uses of simulation and other types of modeling for the purpose of selecting and refining potential strategies, ranging from interventions to investments, to improve the health of communities and the nation's health. Participants worked to identify how modeling could inform population health decision making based on lessons learned from models that have been, or have not been, used successfully, opportunities and barriers to incorporating models into decision making, and data needs and opportunities to leverage existing data and to collect new data for modeling. This report summarizes the presentations and discussions from this workshop.