Time to Change (TTC) is the largest-ever programme in England designed to reduce stigma and discrimination against people with mental health disorders. The TTC evaluation partner is the Institute of Psychiatry at King's College London. We give an overview of the TTC programme 2007-2011 and describe how it was evaluated, by introducing the seven interrelated papers in this supplement, which, taken together, describe a complex series of social interventions using a research design of hitherto unparalleled detail and comprehensiveness.