Cognitive behavioural therapy (CBT) is the dominant model of psychological treatment in the UK and USA. It encompasses a range of approaches underpinned by emphasis on the importance of patterns of thought and behaviour in understanding and alleviating psychological distress. This Very Short Introduction outlines the history of CBT from its origins in behaviour therapy to the present day and explains its theoretical basis. It describes how CBT sessions proceed and the intervention techniques used across a range of problem areas, and considers challenges for the future development of CBT.