Providing a reliable and resilient supply of electric power to communities across the United States has always posed a complex challenge. Utilities must support daily operations to serve a diverse array of customers across a heterogeneous landscape while simultaneously investing in infrastructure to meet future needs, all while juggling an enormous array of competing priorities influenced by costs, capabilities, environmental and social impacts, regulatory requirements, and consumer preferences. A rapid pace of change in technologies, policies and priorities, and consumer needs and behaviors has further compounded this challenge in recent years. The National Academies of Sciences, Engineering, and Medicine convened a workshop on February 3, 2020 to explore strategies for incorporating new technologies, planning and operating strategies, business models, and architectures in the U.S. electric power system. Speakers and participants from industry, government, and academia discussed available models for long-term transmission and distribution planning, as well as the broader context of how these models are used and future opportunities and needs. This publication summarizes the presentations and discussions from the workshop.Table of ContentsFront MatterOverview1 Introduction2 Modeling the Electric System: Approaches and Challenges3 Models for Long-Term Planning4 Models for Transmission Planning5 Models for Distribution System Planning6 Case Study: Los AngelesAppendixesAppendix A: Statement of TaskAppendix B: Workshop AgendaAppendix C: Registered Workshop ParticipantsAppendix D: Acronyms