The functional psychoses 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 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 ICD and 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 historical importance, their influence on current diagnostic systems, their international scope and their scientific importance. The authors provide an indispensable commentary on the ‘Babel of differing formulations in psychiatric diagnosis’, and urge a new ‘polydiagnostic’ approach to psychiatric research, in a book that will be of the greatest value to clinicians and scientific investigators alike.