This text explores how therapists can and must learn from researchers, and how researchers can and must learn from practising therapists. The work is written in dialogue form. A practising therapist, a research psychologist, and a therapy researcher take part in three dialogues, each of which builds on the results of the previous dialogue. The first dialogue explores how therapeutic change takes place, while the second looks at how the mechanisms of action of psychotherapy can be understood in terms of basic psychological concepts. Finally, in the third dialogue, a psychological theory of psychotherapy is developed. The practical implications of this are shown in the form of case examples, as well as guidance on indications and treatment planning. The dialogue ends with suggestions as to how therapy training and provision of psychotherapy could be improved on the basis of the model of psychotherapy that has been developed.