Borderline conditions have been part of psychoanalytical literature since the early stages of psychoanalysis. However, since the second half of the last century, interest in this subject has grown considerably and there has been a steady increase in the number of articles and essays published. Nevertheless, polemic around this theme seems also to grow in the same proportion. This work covers a brief history of the term borderline and some of the controversies in the different psychoanalytical environments, principally as to the relationship between the borderline treatment and that of narcissistic personalities. Issues regarding the constitution of subjectivity and its incidence in the borderline therapy are also dealt with. Finally, some forms of borderline pathology and important clinical aspects, such as transference and counter transference implications, are reviewed. The preference for the term borderline conditions aims to broaden the scope that other terms, such as borderline cases or borderline disturbances may suggest. While these latter possess strong pathological connotations, belonging, therefore, to a specific psychoanalytical treatment, the term borderline conditions allows for the designation of situations with similar characteristics, although episodic and liable to occur in any type of psychoanalytical treatment, including the neurotic.