The Covid-19 pandemic is a generation-defining health crisis. For philosophy of medicine, it casts familiar problems in a new light, while generating new questions about modeling, policy, evidence, values, and expertise. In this issue of Philosophy of Medicine, readers will find a special section of research papers devoted to Covid-19. This section arose from a fourday series of events (online, of course) running 10-13 May 2021, organized in partnership with the Institute for the Future of Knowledge at the University of Johannesburg and the Department of History and Philosophy of Science at the University of Cambridge.In the first of the resulting articles to be published, Maria Cristina Amoretti and Elisabetta Lalumera (2022) critically review the science and limitations of the reproduction number (R) used in pandemic modeling and policy.Lucie White, Philippe van Basshuysen, and Mathias Frisch (2022) defend the initial imposition of lockdown in the UK in 2020 by examining the role of uncertain evidence and poorly constrained epidemiological models in public policy. Their important