The antecedents and risk factors and for developing borderline personality disorder (BPD) are now well documented, but there is a paucity of developmental models to understand the key processes through which they impact on the development of BPD in adolescents. In this article, we present a developmental psychopathology model of BPD in adolescence and link the difficulties adolescents with BPD have with impulsivity and self regulation, with risk factors such as genetic vulnerability, parenting and trauma. We propose a number of psychological processes through which these risk factors undermine personal and interpersonal functioning, and makes it particularly difficult to engage with the challenges of adolescence. These key psychological processes undermine the integration of the self, with extreme unintegrated affects and extreme representations of self and others, undermining the capacity to mentalize. We then make links to possible neurobiological underpinnings of the disturbances in affect, Theory of Mind and interpersonal difficulties in adolescents with BPD.