The National Academies of Sciences, Engineering, and Medicine held a workshop on August 22-23, 2018, in Washington, DC, to explore medical and public health preparedness for a nuclear incident. The event brought together experts from government, nongovernmental organizations, academia, and the private sector to explore current assumptions behind the status of medical and public health preparedness for a nuclear incident, examine potential changes in these assumptions in light of increasing concerns about the use of nuclear warfare, and discuss challenges and opportunities for capacity building in the current threat environment. This publication summarizes the presentations and discussions from the workshop.