To investigate the conceptual base and the factors influencing the process and current practice of psychiatric diagnosis, the authors designed six studies. Clinicians were asked to view a film of a patient interview, rate the patient on a standard set of symptom rating scales, assign a diagnosis, and answer some questions about their backgrounds and specific approach to the diagnostic decision about the case. The results suggest that disagreements among clinicians may be due to actual differences in their perceptions of certain kinds of pathology rather than to semantic preference. Suggestions are offered for methodological and technical improvements in future research in this area.Abstract Teaser