Although psychiatry and psychology have shared an interest in the classification of personality throughout the history of both professions, the efforts of each have largely been independent, with little collaboration or communication. We attempt to bridge this gap by describing a number of research programs in psychology that have implications for the psychiatric diagnosis of personality disorders. We discuss in particular the prototypal model of categorization, the use of behavioral indicators, the identification of prototypic acts, the aggregation of behavior across time and situations, the dimensional model of classification, and the interpersonal circumplex.