Borderline Personality Disorder (BPD) presents a distinct set of challenges within emergency medicine, where acute emotional crises frequently serve as the entry point into the mental healthcare system. Characterized by affective instability, impulsivity, interpersonal hypersensitivity, and chronic suicidality, individuals with BPD often present to emergency departments (EDs) in states of overwhelming distress. These encounters place significant clinical and emotional demands on healthcare providers, especially in environments lacking specialized psychiatric resources. This entry provides a comprehensive framework for the emergency management of BPD, integrating current evidence with ethical, legal, and interpersonal considerations. Clinical presentations are explored in depth, including emotional dysregulation, self-injurious behavior, identity disturbance, and comorbid conditions such as depression, post-traumatic stress disorder (PTSD), and substance use. Emphasis is placed on structured risk assessment, with tools like the Columbia-Suicide Severity Rating Scale and the McLean Screening Instrument aiding in diagnostic clarity and disposition planning. Effective communication and de-escalation strategies are central to this approach. Techniques such as emotional validation, boundary setting, and trauma-informed care help reduce crisis intensity while preserving patient dignity. Pharmacologic interventions are discussed as short-term aids rather than primary treatments, while non-pharmacologic strategies—such as brief dialectical behavior therapy (DBT)-informed approaches—are emphasized as foundational. This entry also addresses the ethical tensions inherent in involuntary treatment, decisional capacity assessment, and the use of coercive measures, urging clinicians to uphold autonomy wherever possible. Multidisciplinary collaboration and provider support mechanisms are highlighted as essential components for sustainable care. By equipping emergency clinicians with practical, compassionate, and evidence-informed tools, this entry aims to improve outcomes for individuals with BPD while promoting a more humane, responsive emergency care system.