The recent and dramatic expansion in studies about borderline and depressive disorders is reviewed with respect to the implications about their interface. Revisiting this subject 6 years after an earlier review reveals that intervening research has altered the conclusions that should be drawn. Growing evidence from family history, comorbidity, phenomenology, psychopharmacology, biological markers, and a new domain, pathogenesis, indicates that a surprisingly weak and nonspecific relationship exists between these disorders. Implications are drawn with respect to classification, therapeutics, and defining the borderline construct.