The Handbook of Behavior Change, edited by Martin S. Hagger, Linda D. Cameron, Kyra Hamilton, Nelli Hankonen, and Taru Lintunen, provides a comprehensive overview of contemporary theories, research methods, and practical approaches for understanding and changing human behavior. Drawing on psychology, sociology, behavioral science, economics, philosophy, and implementation science, the book examines major theoretical models of behavior change and shows how they can be translated into effective interventions. It covers motivation, self-regulation, habits, social and environmental influences, intervention development, implementation, evaluation, and techniques for promoting lasting behavioral change across areas such as health, education, relationships, organizations, and public policy. Written by leading researchers and practitioners, the handbook is designed for psychology students, researchers, clinicians, policymakers, and professionals who need an evidence-based foundation for designing, evaluating, and applying behavior-change interventions.