This chapter provides an overview of the landscape of digital physical activity interventions, encompassing their evolution from early web-based programmes to sophisticated mHealth applications, wearable devices, and gamified approaches. It examines the evidence for their effectiveness, noting the potential for small to moderate improvements in physical activity behaviours, while also acknowledging the nuances across different modalities and the need for more long-term studies. Furthermore, the chapter discusses key theoretical frameworks and models guiding the development and implementation of these interventions, emphasising user-centred design and the use of well-established behaviour change theories. It also introduces intervention types at the forefront of the field, such as just-in-time adaptive interventions (JITAIs), and research study designs required to develop them. Looking ahead, future directions for digital physical activity interventions include a critical focus on addressing the digital divide and ensuring equitable access and effectiveness, enhancing data security and privacy, navigating the complexities of commercialisation, and leveraging the potential of emerging technologies like artificial intelligence and real-time responsive interventions like JITAIs to create more personalised and impactful programmes. Continued research utilising innovative study designs will be crucial to optimise these digital tools for broad public health benefit.