Although the association between trauma and personality disorders, particularly borderline personality disorder (BPD), has been well established, the etiologic role of trauma in the development of personality disorders has been a topic of debate. Numerous mediation models have been put forth to explain how trauma can serve as a risk factor for the subsequent development of BPD. The symptomatic overlap between the proposed complex post-traumatic stress disorder diagnosis and BPD has fueled research efforts aimed at determining whether these are distinct disorders or should both be considered as trauma spectrum disorders. Treatment implications of this diagnostic differentiation are discussed.