This commentary expands on some key issues in the assessment, developmental psychopathology, and treatment of borderline personality disorder (BPD). The authors review evidence suggesting that BPD severity can be assessed along a continuum based on number of DSM criteria, which form a unitary dimension. However, to advance the clinical impact of alternative trait-based dimensional models of BPD, there is a need for measures and clinically validated thresholds that can inform early detection, diagnosis, and treatment planning along the full spectrum of BPD severity and at various stages of its development. They also highlight the importance of longitudinal studies examining dynamic transactional processes contributing to the onset and developmental course of BPD that have implications for individual and family-based interventions and prevention efforts. Regarding treatment, the authors emphasize the importance of addressing functional impairments in major social roles and improving interpersonal relatedness with close attachment figures as valuable means for improving emotion regulation and enhancing long-term recovery and rehabilitation from BPD. Finally, they encourage the use of assessment and analytic strategies capable of modeling idiographic dynamic processes, which may lead to the development of person-specific case conceptualization and treatment approaches.