Clinicians, policy makers and patients are increasingly demanding high quality evidence to help with making decisions about health care. There is a hierarchy of such evidence ranging from anecdote and observational studies up to randomised controlled trials (RCTs). In these trials, the effects of different treatments or other interventions are compared to each other by giving the treatments to patients ‘at random’, thus providing a ‘fair’ and unbiased comparison. RCTs provide much of the evidence needed to register new drugs for use, but trials are also used for comparing a wide range of non-drug treatments, such as medical versus surgical managements for cancer. This course will provide an introduction to the area of clinical trials, with more detailed coverage of some of the key issues to be considered in their design, analysis and interpretation.