Borderline Personality Disorder (BPD) is a severe mental illness. The PRO*BPD-study is the first randomized trial to compare dialectical behavior therapy and schema therapy, the two best evaluated behavior therapy methods. By examining the clinical effectiveness of a broad spectrum of outcome parameters (e.g. BPD-typical symptoms, general psychopathology, comorbidity, quality of life, psychosocial functioning), conducting an economic evaluation and assessing patients’ experiences with qualitative methods, this study will significantly advance our knowledge on psychotherapy for BPD.