Mental retardation does not stand alone as a field for scientific investigation. Its scientific roots lie within the subdivisions of developmental psychology, e.g., intelligence and cognition, attention and habituation, learning theory and behavior principles, language, and psycholinguistics. The understanding of mental retardation is advanced only as far as investigations in the component fields of developmental psychology. Although particular developmental issues may be studied to advantage within the retarded population, developmental psychology is the mirror within which mental retardation must be viewed for scientific purposes. (47 pp.)