Lars-Göran Öst is one of the most eminent clinical researchers in the field of cognitive behaviour therapy (CBT) and a founder of CBT in Sweden. He has recently retired from his position as professor in clinical psychology at Stockholm University, Sweden. In this paper, we sketch a brief description of the body of work by Öst. Examples of his innovative and pioneering new treatment methods include the one-session treatment for specific phobias, as well as applied relaxation for a range of anxiety disorders and health conditions. While Öst remains active in the field, he has contributed significantly to the development and dissemination of CBT in Sweden as well as in the world.