The year 2020 presented extraordinary challenges to organizations working to improve population health - from public health agencies at all levels of government to health systems to community-based non-profit organizations responding to health-related social needs. To improve understanding of how different domains in the population health field are responding to and being changed by two major crises (racial injustice and the COVID-19 pandemic), the Roundtable on Population Health Improvement of the National Academies of Sciences, Engineering, and Medicine held a workshop from September 21-24, 2020, titled Population Health in Challenging Times: Insights from Key Domains. The workshop had sessions organized by themes: academic public health and population health; the social sector; health care, governmental public health; philanthropy; and cross-sector work. Each panel discussion highlighted difficulties and opportunities, both internal to the respective institutions and sectors, and at the interface with peers and partners, especially communities. This publication summarizes the presentations and panel discussions from the workshop.