This book offers an interdisciplinary reflection on the scientific and ethical issues of the notion of proof in medicine. The book poses the following questions: why does an argument convince? How does one make a rational decision in the face of contradictory data? Why and how can we prioritize levels of evidence? What is the value of physicians' professional experience in the production of evidence? By asking these questions, this book highlights the debates surrounding the notions of robustness, relevance and statistical significance regarding different conceptions of the reliability of biomedical knowledge. It is intended for both biomedical scientists (clinicians, epidemiologists, biostatisticians, etc.) and researchers in the social sciences and humanities who are interested in the social organization of clinical trials and in decision-making in a context of uncertainty. It also provides a better understanding of social issues in specific contexts, such as gynecological care, prevention policies, significance tests, and the management of the COVID-19 pandemic.