This chapter reviews the empirical database for STEPPS, which now consists of eight uncontrolled studies and three randomized controlled studies. This provides one of the world’s largest bodies of data supportive of any group treatment for persons with borderline personality disorder, exceeded only by that for dialectical behavior therapy. The data are remarkably consistent in showing that patients have measureable improvements in mood, impulsiveness, and symptoms specific to BPD such as mood instability, cognitive problems (e.g., overvalued ideas, depersonalization, and nonpsychotic paranoia), identity issues, and disturbed relationships; health care seeking and self-harm behaviors are reduced. In correctional settings, STEPPS decreases disruptive behaviors. Further, data show that STEPPS is well accepted by patients and therapists. On the strength of this research evidence, STEPPS has been designated by the United States Substance Abuse and Mental Health Administration as an evidence-based treatment and is listed on the National Registry for Evidence-Based Practices.