Clinical trials have become key technologies for decision making in the contemporary world. Their results shape medical practice and determine priorities across health care systems, but the work that goes into producing credible data is often hidden. Medical Proofs, Social Experiments draws upon detailed case studies to argue that to understand their value, we need to pay more attention to the contexts for these modern medical experiments, recovering the diverse ways in which they involve doctors, patients and the public, the local practices that contribute to their completion, and the complex negotiation of their results in professional and statutory institutions. Presenting research from the UK, USA, Sweden and The Netherlands, the ethnographic perspective adopted by the authors provides a space to explore the investments of different state, market, professional and other actors in particular forms of evaluation, and the ways in which trial methodologies may be re-designed or re-imagined to satisfy social and political expectations. As such, this volume will be of interest to those working in the fields of science and technology studies, the sociology and anthropology of medicine and researchers of policy and organisation in health care.