What does it mean to understand the self in relation to others, and what happens when that system breaks down? This volume brings together leading scholars to explore personality functioning (PF), the core construct underlying the Alternative Model for Personality Disorders and the ICD-11 framework. Although PF has deep roots in psychiatric classification and personality theory, its prominence surged when both diagnostic systems adopted it as the primary criterion for identifying personality disorder. In brief, thought-provoking chapters, contributors share diverse perspectives on how best to conceptualize and measure PF, how it translates to personality pathology, and its utility for clinical assessment and treatment.