Both the understanding of psychopathology and the ability to intervene therapeutically are enhanced by an appreciation of the central role of vicious circles in the development and maintenance of psychological disorder. It is usually possible to discern a structure to people's difficulties in which internal states and external events continually re-create the conditions for the re-occurrence of each other in all too real psychological version of the mythical perpetual motion machine. The present article illustrates how such circular processes work in a number of representative types of psychological difficulty and discusses the implications of this conception for understanding psychopathology and for therapeutic intervention.