What is Borderline Personality Disorder (BPD)? Borderline Personality Disorder (BPD) is a complex and often misunderstood mental health condition that affects an individual’s emotions, behaviors, and relationships. It is categorized as a personality disorder, meaning it involves long-standing patterns of thought, behavior, and interpersonal functioning that differ significantly from cultural expectations. People with BPD often experience intense and fluctuating emotions, instability in their self-image, and difficulty in forming and maintaining stable relationships.