Digital health behavior interventions have the potential to reach many people at low cost and in remote locations, contributing to promoting health for all. However, the reach of digital health behavior interventions is currently limited, and many interventions are quickly abandoned, which limits their effectiveness. A number of factors contribute to the limited uptake of and engagement with digital health behavior interventions, including limited availability and access, psychological factors (e.g., knowledge, motivation), the technology itself (e.g., usability, privacy), and social influences (e.g., recommendations, stigmatization). Stakeholders, including intervention developers and policymakers, can use this knowledge to identify strategies to overcome these barriers and design improved digital health behavior interventions that attract more users and engage them for prolonged periods. In this vein, they will help to promote health behaviors at scale.