Four different models of Borderline Personality Disorder (BPD), each based on a different psychopathological theory, have produced manualized treatments and on this basis controlled outcome studies that evidenced their efficacy. It can be argued, on the ground of the comparable results of the outcome studies, that these different treatments share a common mechanism of action related to the same psychopathological kernel of BPD . The hypothesis that such a psychopathological kernel can be described as dissociative and caused by chronic psychological traumatization in the developmental years allows for a synthetic description of the basic psychotherapy processes allegedly shared by the four different models of BPD treatment.