The person with a borderline personality is considered to be neither neurotic nor psychotic, but to exist somewhere in between these two diagnostic categories. Psychoanalytic theorists who have researched the phenomenon of the borderline personality have shifted their emphasis away from Freud's instinct psychology and toward an ego psychology perspective. The Diagnostic and Statistical Manual of Mental Disorders-III lists eight specific symptoms of the borderline personality, of which at least five must be present to allow the diagnosis of borderline personality disorder: impulsivity or unpredictability in at least two potentially self-damaging areas; intense and unstable interpersonal relationships; inappropriate anger; identity disturbance; affective instability characterized by mood swings; intolerance of being alone; physically damaging acts; and chronic feelings of emptiness and boredom. Borderline personality disorders are generally global, affecting all areas of life. Patients with borderline personality disorders tend to blame others for their predicament; are often untroubled by their illness; and have rigid, inflexible, and maladaptive personality traits. This paper presents the psychoanalytic theory of borderline personality development, concentrating on the work of Kernberg and Masterson as perhaps being most representative of the new approach. The paper then goes on to present an Adlerian model of the borderline personality which takes the similarities with analytic theory into account. Conceptual differences that separate and differentiate the Adlerian model from psychoanalytic theory are also addressed. (NB)