Advance Care Planning(ACP)has long been a staple of caring for people with serious illness. Over its history, it has been defined in different ways. Clinicians, researchers, patients, and the public have developed a variety of perspectives about the many aspects of ACP, ranging from the definition to the timing, goals, outcomes, and value of ACP. To better understand the challenges and opportunities for ACP, acknowledge and highlight divergent viewpoints, and examine what is empirically known and not known about ACP and its outcomes, the National Academies of Sciences, Engineering, and Medicine's Roundtable on Quality Care for People with Serious Illness hosted a virtual public workshop, Advance Care Planning: Challenges and Opportunities, on October 26 and November 2, 2020. The workshop explored the paradox of ACP, its evidence base, ways to think differently about ACP, and various approaches to making it more effective.This Proceedings of a Workshop summarizes the presentations and discussions from that workshop. Table of Contents Front Matter Proceedings of a Workshop Appendix A: Statement of Task Appendix B: Workshop Agenda