The present report begins with a review of the literature and proceeds through a discussion which develops models for three major classes of. affective disturbance: normal grief, primary depression, and mania. Primary depressions are seen to comprise two major subclasses: the bipolar manic depressive disorders and the unipolar depression. The manifestations of manic depressive disorder are examined from a genetic standpoint which involves epidemiological considerations. The depressive disorders are further considered from the standpoint of a distinction between pure depression and a depressive spectrum. These concepts are examined in terms of such considerations as age and sex, and a distinction between females with an early onset and males with a late onset is emphasized. The proposed classification of depression relies on familial constellations of affective illness.