Mentalization-based therapy (MBT) is increasingly being considered as a treatment for people with borderline personality disorder (BPD), and a systematic review was required to investigate its effectiveness. MBT was found to be equally as effective or superior to well-established comparison treatments of BPD, however, the majority of studies was of unsatisfying quality. Little is known about the mechanisms of MBT. Further, better quality trials are needed to investigate its efficacy in treating BPD.