mean, what do they predict, and how well do they predict it? (Section 2) • Why do individuals differ in intelligence, and especially in their scores on intelligence tests? Our discussion of these questions implicates both genetic factors (Section 3) and environmental factors (Section 4). • Do various ethnic groups display different patterns of performance on intelligence tests, and if so what might explain those differences? (Section 5) • What significant scientific issues are presently unresolved? (Section 6) Public discussion of these issues has been especially vigorous since the 1994 publication of Herrnstein and Murray's The Bell Curve, a controversial volume which stimulated many equally controversial reviews and replies. Nevertheless, we do not directly enter that debate. Herrnstein and Murray (and many of their critics) have gone well beyond the scientific findings, making explicit recommendations on various aspects of public policy. Our concern here, however, is with science rather than policy. The charge to our Task Force was to prepare a dispassionate survey of the state of the art: to make clear what has been scientifically established, what is presently in dispute, and what is still unknown. In fulfilling that charge, the only recommendations we shall make are for further research and calmer debate.