The available empirical evidence concerning the etiology of borderline personality disorder is reviewed. A tripartite model of the development of BPD is then presented. This model has three elements: a traumatic childhood (broadly defined), a vulnerable (hyperbolic) temperament, and a triggering event or series of events. The authors conclude that each borderline patient has a unique pathway to the development of BPD that is a painful variation on an unfortunate but familiar theme.