The Handbook of Behavior Change is the first wide-ranging compendium of theory- and evidence-based research and practice on behavior change. It provides scientists, students, and practitioners with the current evidence on behavior change and expert advice on how to develop, evaluate, and implement behavior change interventions. The handbook also sets an agenda for future research on behavior change theory and practice across multiple behaviors, contexts, and populations. This chapter outlines emerging issues and future research directions arising from the handbook. The chapter stresses the importance of theory development, including the need for greater emphasis on ecological and social theories; clearer descriptions and operationalizations of behavior change theories; and increased application of interdisciplinary approaches. Future research on intervention development should conduct more comprehensive intervention fidelity assessments; adopt novel means to improve the translation, feasibility, and optimization of interventions; ensure consideration of ethical issues in behavior change research; routinely evaluate mechanisms of action in behavior change interventions; and apply complex systems approaches to behavior change. “Best-practice” guidance on behavior change should consider emerging methods and approaches to behavior change; implement trials to evaluate the long-term maintenance of behavior change; and develop core curricula on behavior change to educate the next generation of scientists and practitioners.