One of psychology's outstanding successes has been the measurement of intelligence, and the demonstration that differences in intelligence, so measured, were due in large part of genetic factors. In recent years much work has been done to clarify the problem of the biological basis of these inherited differences, and work on the evoked potential in the EEG has generated important new findings in this field. We now know far more about intelligence, its inheritance, and its biological basis than we did even a few years ago.