In DSM-5, there are two classification frameworks presented for diagnosing borderline personality disorder (BPD). The first is in Section II of the manual and presents the historical, medical-categorical diagnostic criteria, unchanged from DSM-IV. In Section III of the DSM-5, which presents Emerging Measures and Models, there is a novel, trait-based model for diagnosing personality disorders (PDs), and a trait-based diagnostic criteria-set for BPD. This hybrid model represents a transition from the traditional, categorical diagnosis to a dimensional model of classification. In this chapter, we discuss the motivations for these changes in diagnosing PDs, and specifically, the impact that such changes could have for how we conceptualize, research, and treat BPD. In particular, moving toward a more dimensional model could have positive repercussions for how we provide services to children and adolescents who are suffering from BPD or BPD traits.