There have been many changes to the regulation of health professionals (like doctors, nurses and therapists) in England over the last decade, intended to protect the public by ensuring professionals are fit to practise and making them accountable through effective regulatory arrangements. In the past, once they had qualified, health professionals were subject to little or no scrutiny during their career unless their performance gave cause for concerns or there were complaints about them. After more than a decade of debate and development, in 2012 the General Medical Council introduced a new requirement for all doctors to be “revalidated” at least once every five years while they hold a licence to practise. This involves the appraisal of their performance and is usually undertaken by their employer. Medical revalidation is a major change to the regulation of doctors, and its implementation is being watched with interest by other health professions regulators who are considering similar requirements for nurses, therapists and other groups. Our research sets out to see how the new arrangements for medical revalidation are being implemented both in the NHS and more widely, and to see how they are used to assure and improve medical performance. We will use a number of sources of data including national surveys of organisations which employ doctors; case studies of a selection of different types of organisations involving interviews, observation and documentary analysis; surveys of doctors undergoing revalidation in those organisations; detailed casework on examples of suboptimal medical performance and how they were managed; and the analysis of large existing data sets on doctors working in the NHS acute sector and their performance. Overall, our findings about how revalidation works, the way it has been implemented, and its costs and impacts, will be of great use in the refinement and future development of revalidation and similar initiatives to the General Medical Council and other health professions regulators, to the Department of Health in England and government in the other countries of the UK, and to regulators and health professions in other countries.