The American concept of schizophrenia is built primarily upon concepts advanced by Kraepelin, Bleuler, and Schneider. Because of the influence of major research studies such as the International Pilot Study of Schizophrenia and the U.S./U.K. study, emphasis has been placed on developing reliable descriptions of symptoms and a precise definition of the disorder. This research also led to a recognition that the American concept of schizophrenia was relatively broad in comparison with that used in the rest of the world. This led to a critical reappraisal of American diagnostic practices during the 1970's, culminating in the narrower definition of schizophrenia in the third edition of the Diagnostic and Statistical Manual of the American Psychiatric Association (DSM-III). This definition requires the presence of psychotic features, established chronicity, evidence of deterioration, and the exclusion of affective and "organic" features. In comparison with this definition, the Soviet concept appears to be much broader and to include non-psychotic forms. Treatment implications of these differences are discussed.