Crowell, Kaliush, and Vlisides-Henry (this volume) provide a thought provoking chapter on assessment of mechanisms in personality disorders and describe the notable advancements for estimating genetic, temperamental, and environmental factors that arguably contribute to their development. To expand the depth and breadth of the target chapter, this commentary argues for a focus on the reciprocal and dynamic transactional processes that occur between an individual (genetic risk factors) and their environment. In this comment, the authors integrate findings from the broader genetics, personality, and psychopathology literature to illustrate the role of transactional mechanisms in developmental pathways to borderline personality disorder (BPD). Additionally, the authors highlight current gaps in the extant literature and discuss ways in which future research can investigate the person-environment transactions associated with BPD and related psychopathology. In addition to building our understanding of vulnerability to developing BPD, there are considerable prevention implications that may result from detection of malleable individual-based contributing factors to environmental exposure that may in turn reduce the risk of environmental stressor exposure in vulnerable individuals.