This book addresses the process and actions for developing enhanced capabilities to analyze energy policy issues and perform strategic planning activities at the U.S. Department of Energy (DOE) on an ongoing basis. Within the broader context of useful analytical and modeling capabilities within and outside the DOE, this volume examines the requirements that a National Energy Modeling System (NEMS) should fulfill, presents an overall architecture for a NEMS, identifies data needs, and outlines priority actions for timely implementation of the system.