Approximately five percent of Medicare beneficiaries (2.2 million Americans) are living with serious illness, as are many other non-Medicare eligible individuals. This number is expected to grow rapidly as the population ages and the prevalence of progressive illness increases. In many communities, particularly urban and rural underserved communities, primary care clinicians are the main workforce caring for people with serious illness, which underscores the need to integrate high quality serious illness care into primary care delivery. To better understand the challenges and opportunities for integrating serious illness care into primary care settings, the National Academies of Sciences, Engineering, and Medicine's Roundtable on Quality Care for People with Serious Illness hosted a virtual workshop on June 10 and 17, 2021. The workshop, titled Integrating Serious Illness Care into Primary Care Delivery, explored the shared principles of primary and serious illness care, the interdisciplinary teams that power both disciplines, the policy issues that can act as barriers to or incentives for integration, and best practices for integrating primary care and serious illness care. This Proceedings of a Workshop summarizes the presentations and discussions that occurred during the workshop.