Dynamic systems theory provides a conceptual framework for the study of change in psychotherapy that is consistent with that used in other sciences. A dynamic systems model of change was proposed and evaluated in the context of cognitive therapy for depression. Consistent with this model, less client protection and more destabilization of depressive patterns predicted more improvement at the end of treatment. Less protection was associated with more therapist support/stabilization. More destabilization was associated with more affective intensity in the session and with more of a therapist focus on the historical antecedents of current problems, exposure to multiple sources of corrective information, and repeated practice of new skills. Although preliminary, this pattern of findings is consistent with the model proposed and with principles of dynamic systems from other sciences.