"This book describes the theory and methodology of eliciting and measuring psychopathology and the ways in which the signs and symptoms of mental disorder are combined into diagnostic categories. Mental disorders are classified and measured to allow clinicians to communicate with one another about the patients' symptoms, prognosis, and treatment and to ensure that research is conducted with comparable groups of subjects." Essential reading for clinicians and non-clinical scientists engaged in research on psychiatric disorders, trainees and junior psychiatrists, and clinical psychologists.