Characterized by a combination of interpersonal, emotional, behavioral, and cognitive instability, borderline personality disorder (BPD) is a serious and often misunderstood condition. The prevalence of BPD is approximately 1.4 to 6%, with substantially higher estimates among psychiatric outpatients and inpatients. Beyond the personal costs of BPD in terms of suffering, BPD is strongly associated with functional impairment and high societal costs for mental healthcare. Clinical descriptions of BPD first appeared before the mid-twentieth century and have evolved to the present conceptualization of an overarching BPD construct represented by the key domains of emotion dysregulation, impulsivity, and interpersonal disturbance. BPD has a varying course, with many individuals achieving remission or recovery, but emotional and interpersonal vulnerabilities and functional impairments often persist for many years, even after structured treatment. The success of treatment for BPD over the past few decades, however, has countered common clinical lore that BPD patients are recalcitrant. Further, novel developments in research on the putative core vulnerabilities underlying BPD, as well as evidence that these vulnerabilities can be addressed in treatment, illuminate important future directions and hope for patients and loved ones affected by this disorder.