According to Jon Karlsson, the influence of genetic factors on human mentality has been neglected for many years in the study of intelligence. He contends that the evidence for biological influences on human intelligence is too compelling to be ignored any longer. Karlsson believes that such influences can be positive, and that ways can be found to measure their importance. Serious efforts are necessary to extend the scope of basic conceptions concerning the structure of the brain and to explore the mysteries of the physiological mechanisms that govern the human mind. The research reported in this volume suggests some approaches that might prove useful. Karlsson believes that an effective approach to the genetics of mentality can be built around studies of serious brain abnormalities. Beginning with the idea that psychosis probably has a genetic bond to creativity, he argues that parallel possibilities exist in relation to other frequently occurring disorders. The product of many years of research, this work is certain to be a source of both controversy and of new ideas for the study of human intellectual development.