In the past twenty years, attachment research with children and adults has yielded a lot of information on how implicit relational patterns are transferred from parents to their children in the first year of life. A psychoanalytic theory, useful for the treatment of Borderline Personality disorder, and which complements the classical theories is proposed on the basis of these data . A central concept in this theory is the development of a coherent self-as-agent and the development of the capacity to mentalize. This is the capacity to understand and to reflect on our own feelings, ideas and intentions as well as those of others. In neurosis the focus of treatment may be mental representation disorder, conflicting mental representations, but with borderline patients the focus has to be the mental process-disorder and the furthering of the development of mentalizing skills. This distinction has consequences for the technique of treatment.