The functional psychoses, medical diseases with no known biological causes (for example, schizophrenia and anxiety disorders), continue to be classed as illnesses of unknown origin, and the validity of diagnostic concepts therefore also depends on extrinsic criteria such as course and outcome, results of biological and genetic investigation, and response to treatment. Operational diagnostic criteria, or the process of defining a psychosis by studying its manifestations, are the main subject of this book, which presents a comprehensive review of the present state of diagnostic formulations for functional psychoses. From the early nosological and pathogenetic concepts of Kraepelin, Bleuler. Schneider, and Kasanin, the authors trace the development, internationally, of the various classifications of the functional psychoses, culminating among others in those embodied in the latest International Classification of Diseases (ICD) and Diagnostic and Statistical Manual (DSM) formulations. This is a revised and expanded edition of Diagnostic Criteria for Schizophrenic and Affective Psychoses and is also published under the auspices of the World Psychiatric Association. Diagnostic criteria have been selected for inclusion on the basis of their historic importance, their influence on current diagnostic systems, their international scope, and their scientific importance.