Recent studies identify a much higher incidence of postpartum depression than had previously been acknowledged and show that a mother's depression may have a highly deleterious effect on the early development of her infant. Although a variety of theories exist concerning the etiology of postpartum depression, many writers now accept a transactional model of causality. This article suggests that for many women early depriving or abusive experiences are necessary but not sufficient conditions to explain the development of severe postpartum depression. Four different types of postpartum depression are presented with widely differing prognoses and needs for treatment. It is suggested that a wide range of treatment modalities may be needed with the more serious depressions and that such services are lacking in most communities.