Objective: To provide understanding into the biological basis of thinking and behavior in people with personality disorders, explain anatomic findings, and appraise therapeutic options. Data Sources: PubMed was searched with no date restrictions using the terms personality disorders DSM-5, cluster B personality disorders, biological psychiatry of personality disorders, neurobiology of personality disorders, and neurobiology of cluster B personality disorders. Study Selection/Data Extraction: We identified 2,790 English-language articles and utilized 18 in this report. Results: There are anatomic features typical to the brains of individuals with cluster B personality disorders, for example, abnormalities in the superior frontal cortex and amygdala and enlarged striatal volumes. Emotional dysregulation and impulsiveness are 2 prominent symptoms. Hereditary factors may contribute to the development of such conditions. Conclusion: Understanding the neurobiology of cluster B personality disorders expands knowledge that hopefully results in better clinical management and development of improved treatments. Psychotherapy is currently the most effective intervention for borderline personality disorders. Symptomatic pharmacotherapies may be prescribed adjunctively on an individualized basis if clinically indicated (eg, with a coexistant depression).