manic-depressive illness can confer advantages on both the individual and society. The disease, in both its severe and less severe forms, appears to convey its advantages not only through its relationship to the artistic temperament and imagination, but through its influence on many eminent scientists, as well as business, religious, military, and political leaders. Subtler effects--such as those on personality, thinking style, and energy--are also involved because it is a common illness with a wide range of temperamental, behavioral, and cognitive expression.