Robust development of behavior change interventions is based on a sound understanding of the target group, the target behaviors that need to change, the context in which change will occur, the hypothesized mechanisms of change, and the behavior change techniques. Intervention development frameworks advocate a systematic approach to behavior change intervention development. Key tasks include (1) identify and analyze the problem addressed in behavioral terms; (2) identify intervention mechanisms, content, and delivery mode(s) and design a logic model or program theory; (3) develop materials or prototypes (e.g., interface); and (4) test the intervention iteratively through empirical optimization. The tasks apply to both developing new interventions and optimizing existing interventions. The tasks may differ somewhat for digital behavior change interventions (e.g., iterative testing and refinement of early prototypes during development). Depending on time and resources, the tasks can be completed relatively quickly or take considerable time. The current chapter presents key challenges in intervention development and describes potential solutions. Fidelity, feasibility, and acceptability should be considered during all development tasks. The chapter also provides recommendations for advancing the methodology of intervention development and the use of intervention development frameworks and approaches in practice and policy settings.