The introduction offers an overview of the ways in which conflict of interest (COI) is affecting the world of medicine and details the methodological and analytical choices this edited book is based upon. Starting from the COVID-19 pandemic case, it first shows how conflict of interest issues impact the scientific controversies in the sector of biomedicine, its professions, the functioning of its organizations (research institutes, regulatory agencies and ministries, medical journals, patient organizations, etc.), patients’ trust in treatments and public decisions, but also the political struggles inside the field. The introduction then demonstrates that the existing literature on COI has favoured normative or quantitative perspectives and that, partly because of the perception that COI is mainly an “insider category”, infused with idealized professional norms of purity, social science researchers have been reluctant to consider COI as a fruitful subject through which to study science and medicine. After having presented the few works conducted on COI in social sciences, the introduction presents the methodological and analytical strategy adopted in the book. The contributions brought together in this volume are rooted in the social sciences (sociology, history, political science and legal studies) and are based on solid empirical work, that focuses on the actors involved, their practices and the social dynamics at play. Their analyses combine two lines of investigation. The first one consists in analyzing the socio-historical construction of COI as a social category, its heterogeneous usages across time, countries and social spaces, and the different kinds of laws or procedures built in the name of COI; the second one focuses on examining the changing nature of the arrangements between corporate interest and health actors, their consequences and the way health professionals or scientists perceive them. The introduction then (re)place COI-related debates and processes within larger social dynamics that have affected the world of public health for several decades, the main ones being the transformations of the political economy of pharmaceutical knowledge, the politicization and scandalization of public health risks, and the development of a transparency movement in science and politics. In the last section, the introduction presents the structure of the book and its different contributions.