The author reviews the psychodynamics and developmental psychology of the borderline patient as described in the literature on intensive therapy, early mother-child interaction, and family interaction. Focusing on the borderline patient's characteristic difficulties in intimate relationships, he describes the patient's use of splitting and projective identification as seen in the characteristic transference-countertransference interaction in intensive therapy. These primitive defensive mechanisms, which are also utilized by family members, appear to contribute to a failure of empathic responses both during the child's early development and in the family interactions during the child's adolescence. The author concludes that conceptual attempts to relate adult and child phenomena, although highly speculative, create new and useful perspectives for the treatment of borderline patients.