Drawing on the statistical and philosophical expertise of its authors, this book is designed to improve understanding and use of randomised controlled trials (RCTs) among health professionals. It is intended for use primarily by medical educators involved in teaching statistics and evidence-based medicine (EBM) to medical students, junior doctors and other health professionals. However, each of the chapters serves a wider range of interests, including the practical needs of physicians in interpreting research evidence to support clinical decision making and the teaching needs of  philosophers of medicine who want to more fully appreciate how RCTs work in practice and provide engaging examples for their students. Rather than compete with the proliferating methodological literature on RCT designs, this book focuses on cultivating a healthy skepticism among developing health professionals to support critical appraisal of their own and published work on RCTs at a fundamental level, including through a more informed understanding of the place of subgroup analyses in sound statistical inference. Management of the positive predictive value in the statistical analysis of RCT findings is included as an important topic for contemporary medical curricula.  In comparing  RCTs with non-randomised studies, a search for empirical evidence for the superiority of RCTs is initiated, pointing to the need for further work to confirm what form this evidence should take. Medical educators will find a wealth of reasons to encourage their students to think more critically about how the RCT operates in practice as a gold standard.