The COVID-19 crisis has transformed the highly specialized issue of what constitutes reliable medical evidence into a topic of public concern and debate. This book interrogates the assumption that evidence means the same thing to different constituencies and in different contexts. Rather than treating various practices of knowledge as rational or irrational in purely scientific terms, it explains the controversies surrounding COVID-19 by drawing on a theoretical framework that recognizes different types of rationality, and hence plural conceptualizations of evidence. Debates within and beyond the medical establishment on the efficacy of measures such as mandatory face masks are examined in detail, as are various degrees of hesitancy towards vaccines. The authors demonstrate that it is ultimately through narratives that knowledge about medical and other phenomena is communicated to others, enters the public space, and provokes discussion and disagreements. This title is also available as Open Access on Cambridge Core.