This chapter provides an update of the mentalizing approach to borderline personality disorder (
BPD
). We present a multilevel approach to
BPD
from a developmental psychopathology life‐span perspective, discussing developmental pathways involved in the emergence of
BPD
from infancy to adolescence and (young) adulthood, locating the origins of the social cognition or mentalizing impairments typical of
BPD
patients in attachment disruptions. We also discuss in this context emerging findings stressing the importance of gene–environment transactions in
BPD
, and research findings concerning the neurobiology of impairments in mentalizing and attachment in these patients. Finally, we outline mentalization‐based treatment for
BPD
and we present a new view on the mechanisms of change in the treatment of
BPD
rooted in extant theories concerning the intergenerational transmission of social knowledge and social learning, suggesting that this mechanism may be the missing link that connects and is shared by all effective treatments of
BPD
.