This text aims to provide a clear, accessible study of the contributions and influence of Aaron Beck, Professor of Psychiatry at the University of Pennsylvania School of Medicine, USA, and part of the cognitive revolution in psychotherapy. The author reviews the influences on which Beck drew during a time of great change, and rebuts the criticisms his work has attracted It is suitable for professional and trainee counsellors, psychotherapists, counselling psychologists, clinical psychologists, psychiatrists and social workers.