The Oxford Handbook of Self-Determination Theory, edited by Richard M. Ryan, provides a comprehensive account of Self-Determination Theory (SDT), one of the major frameworks for understanding human motivation, personality development, and psychological well-being. Drawing on more than four decades of research, the handbook examines SDT’s six mini-theories and its central concepts of autonomy, competence, and relatedness, while exploring intrinsic and extrinsic motivation, internalization, vitality, mindfulness, relationships, culture, personality, and human flourishing. Its 57 chapters also examine applications of SDT in education, parenting, organizations, healthcare, sport, psychotherapy, and other areas of life. Written by leading researchers in the field and edited by one of SDT’s co-founders, the volume is designed for psychology students, researchers, clinicians, educators, and professionals seeking an evidence-based understanding of motivation and the social conditions that support healthy psychological functioning.