Borderline personality disorder (BPD) was introduced in the DSM‐III in 1980. From the DSM‐III to the DSM‐5, no major changes have occurred in its defining criteria. The disorder is characterized by instability of self‐image, interpersonal relationships and affects. Further symptoms include impulsivity, intense anger, feelings of emptiness, strong abandonment fears, suicidal or self‐mutilation behavior, and transient stress‐related paranoid ideation or severe dissociative symptoms. There is evidence that BPD can be reliably diagnosed and differentiated from other mental disorders by semi‐structured interviews. The disorder is associated with considerable functional impairment, intensive treatment utilization, and high societal costs. The risk of self‐mutilation and suicide is high. In the general adult population, the lifetime prevalence of BPD has been reported to be from 0.7 to 2.7%, while its prevalence is about 12% in outpatient and 22% in inpatient psychiatric services. BPD is significantly associated with other mental disorders, including depressive disorders, substance use disorders, post‐traumatic stress disorder, attention‐deficit/hyperactivity disorder, bipolar disorder, bulimia nervosa, and other personality disorders. There is convincing evidence to suggest that the interaction between genetic factors and adverse childhood experiences plays a central role in the etiology of BPD. In spite of considerable research, the neurobiological underpinnings of the disorder remain to be clarified. Psychotherapy is the treatment of choice for BPD. Various approaches have been empirically supported in randomized controlled trials, including dialectical behavior therapy, mentalization‐based therapy, transference‐focused therapy, and schema therapy. No approach has proved to be superior to others. Compared to treatment as usual, psychotherapy has proved to be more efficacious, with effect sizes between 0.50 and 0.65 with regard to core BPD symptom severity. However, almost half of the patients do not respond sufficiently to psychotherapy, and further research in this area is warranted. It is not clear whether some patients may benefit more from one psychotherapeutic approach than from others. No evidence is available consistently showing that any psychoactive medication is efficacious for the core features of BPD. For discrete and severe comorbid anxiety or depressive symptoms or psychotic‐like features, pharmacotherapy may be useful. Early diagnosis and treatment of BPD can reduce individual suffering and societal costs. However, more high‐quality studies are required, in both adolescents and adults. This review provides a comprehensive update of the BPD diagnosis and clinical characterization, risk factors, neurobiology, cognition, and management. It also discusses the current controversies concerning the disorder, and highlights the areas in which further research is needed.