A systematic review and critique of the work of midlife researchers and theorists such as Gould, Vaillant, Jung, Newman and Levinson, among others, indicates that: (1) a midlife transition period exists from approximately 35 to 55 and lasts as many as 10 years for both men and women; (2) a series of unique and fundamental biological, psychosocial, interpersonal, and developmental tasks occur during midlife transition; (3) a major reassessment of personal functioning, primary relationships, and the world of work often occurs in this period; and (4) the emergence at midlife of the expressive parts of the personality for men and the instrumental components for women represents a major source of personal and marital stress. (Author)