In the past, definitions of mental retardation rested on IQ test scores, and experts favored segregation and separate classes. But today the pejorative idiotimbecile-moron classification system has been replaced by more descriptive terms (mild, moderate, severe, profound); IQ as a predictor of adult success has been discredited; and normalization (small residences, mainstreaming) is the more commonly pursued policy. Edgerton's concentrated, impressively selective overview investigates the known and suspected causes of retardation, distinguishes between clinical and sociocultural retardation, and summarizes the research findings which have nearly reversed professional attitudes in recent years. It's a notable effort, embracing both hard facts and salient details, which unequivocally flags the knotty issues: sexuality, work, independence. And Edgerton repeatedly measures the evidence. He reports, for example, on malnutrition studies involving rats but qualifies their significance, noting key physiological differences and other research obstructions: ""it is no simple matter to determine whether a rat is mentally retarded."" Or he outlines the auspicious results of the Milwaukee (enrichment) Project and also includes the ""hothouse effect"" charges. And throughout, he keeps his guns leveled at the various insufficiencies of IQ tests, which doubly discriminate against ethnic minorities and which, while useful as a gauge of school performance, fail to register more important competencies--community adjustment, say, or overall reliability. In little more than 100 pages, it covers the field and establishes its own authority within it.