The Personality Disorder Institute/Borderline Personality Disorder Research Foundation randomized control trial (PDI/BPDRF RCT) is a controlled outcome study for borderline personality disorder (BPD), in which 90 participants were randomized to one of three manualized and monitored, active psychosocial treatment conditions. These treatments are: (a) Transference-Focused Psychotherapy (TFP; Clarkin, Yeomans, & Kernberg, 1999), a treatment for BPD based on object-relational and psychoanalytic principles first applied to BPD by Kernberg (1996), notable for its particular emphasis on interpretation of object relations activated in the ongoing therapeutic relationship; (b) Dialectical Behavior Therapy (DBT; Linehan, 1993), a popular treatment for BPD, with evidence of efficacy (Linehan, Armstrong, Suarez, Allmon, & Heard, 1991) that emphasizes a balance between acceptance and change in its combination of cognitive-behavioral and Zen principles; and (c) supportive psychotherapy (Rockland, 1992), another object-relational and psychoanalytically based treatment for BPD which, in contrast to TFP, eschews transference interpretation and places primary emphasis on development of a collaborative engagement with the patient to foster identity development. Patients received medication, if clearly indicated, according to the treatment algorithm developed by Soloff (2000). This article describes the significance and rationale of the study and the overall design, methods, plan of analysis, and demographic characteristics of the recruited sample of patients.