While the DSM-5 retains a categorical model of personality disorders, and the ICD-11 has moved to a fully dimensional model, an alternative hybrid model embodies the best of both worlds. This volume presents the latest theory and research on the diagnosis and treatment of personality disorders. It describes changes in the DSM-5 and ICD-11 assessment of personality disorders, reviews empirical support for these changes, and provides clinical guidance for diagnosing and treating the most common personality disorders. A primary focus throughout the book is the Alternative Model for Personality Disorders (AMPD), found in Section III (Emerging Measures and Models) of the DSM-5. The AMPD is a hybrid of the earlier categorical model of personality disorders and the emerging dimensional model fully embraced in the ICD-11. The AMPD offers a middle-of-the-road approach that is supported by a growing body of research, and it has shown significant promise in clinical use. With its blend of research, clinical guidance, and case studies, this volume will be an essential resource for clinicians and researchers who study and treat the most complex and intractable of mental health problems.