Workplace-based assessment is a core element of the changes introduced in Modernising Medical Careers (MMC), yet it has been sparsely researched in the UK and there are still psychometric and validity data needed to support its introduction. Supervisors and tutors are wary of it, but it could replace external clinical examinations leading to a Certificate of Completion of Training. The theoretical background of assessment in the workplace is ‘Miller's pyramid’ of competence in which the trainee progresses from ‘knowing’ (tested by paper exam), through ‘knows how’, to ‘shows how’ (tested by the Observed Standardised Clinical Examination), and finally ‘does’ (assessed in the workplace) (Miller, 1990).