We present the hypothesis that the laws of thermodynamics can be usefully applied to psychotherapy. In this model psychotherapy is presented as a means of entropy management, whereby the patient trades entropy (in this case the expressed symptoms of mental disorder) with the therapist. The therapist serves to increase the capacity of the patient, both through developing a shared understanding of the challenges the patient faces and through generating shared solutions. This process can be understood in terms of entropy trade where energy is successfully redirected into adaptive behaviour. The hypothesis and proposed model of psychotherapy are evaluated in the context of current thinking about the components of successful psychotherapeutic outcomes; including evidence based practice, therapist competence and adherence and the therapeutic alliance.