A great deal has been written about the nature of borderline personality. We maintain that borderline psychopathology emanates from particular disturbances in mental representations-impairment in the ability to maintain and use benign and integrated internal images of self and others-and that these troubled ways of thinking drive the troubled interpersonal relations, affective instability, and impulsivity associated with borderline. Aspects of borderline self-other representational disturbances are present across a wide theoretical spectrum, and a number of research methodologies already exist to assess the phenomena. We conclude that borderline attributes exist on continua, and summarize important features as: (1) unstable mental images of self and others, often marked by self-loathing and attributions of malevolence to others; (2) interactions with others organized around a fundamental need for care that is felt to be necessary for basic functioning; (3) fear of others based on expectations of being mistreated and disappointed and/or terror of having one's identity subsumed by another person; (4) difficulty considering multiple and/or conflicting perspectives, with a tendency toward concrete, all-or-none, or black-and-white, thinking and distortion of reality; and (5) sadomasochistic interpersonal interactions in which a person alternatively inflicts suffering on others and suffers at the hands of others.