The aim of the Special Section that this paper contributes to is to review current trends in borderline personality disorder (BPD) research. Three major trends were identified. First, there has been a marked increase in studies that attempt to locate BPD in the dimensional latent structure of psychopathology. Second, identifying the endophenotypic markers associated with BPD has become a focus of interest. Here, we focus on one endophenotype in the form of impaired self-other processing. Third, there has been an explosion of research into the developmental aspects of BPD specifically focused on uncovering complex Biology × Environment interactions in the development of BPD. This paper discusses how these trends (Dimensions, Biology, and Development) are challenging the nature and form of BPD as we know it, and may be indicative of a broader sea-change in psychiatric nosology.