Cognitive behaviour therapy is arguably the most well-known, most widely used and most accessible form of talking therapy in the Western world. It has been adopted by the NHS as the mainstay of its IAPT primary care therapy programme. It converts readily and successfully into online formats and self-help programmes. In this updated introduction to CBT, three of its foremost proponents and practitioners summarise its origins, principles, how it works in practice, and the research that underpins its widespread use. This second, revised edition updates the research and includes the third and fourth ‘waves’ of cognitive behaviour approaches and other more recent developments that have emerged since the first edition was published.