In cognitive analytic therapy (CAT), multiplicity is understood in terms of a range of self-other patterns (reciprocal role relationships) originating in childhood. These alternate in determining experience and action according to the situation (contextual multiplicity). They may be restricted by adverse childhood experiences (diminished multiplicity), and severe deprivation or abuse may result in a structural dissociation of self-processes ( pathological multiplicity). Therapeutic interventions, to be effective, must be based on an understanding of the structure of the individual patient's self-processes. In CAT practice, descriptions of dysfunctional relationship patterns and of transitions between them are worked out by therapist and patient at the start of therapy and are used by both throughout its course. This approach is illustrated by an account of the treatment of a depressed and anxious 70-year-old man who alternated between two main patterns. © 2007 Wiley Periodicals, Inc. J Clin Psychol: In Session 63: 165–174, 2007.