The integration of patient and public involvement (PPI) in the development of digital health interventions (DHI) is essential for ensuring usability, engagement, and long-term adoption. While human-centered design (HCD) has been widely applied, its inconsistent implementation has led to interventions that fail to meet real-world patient needs, contributing to low adherence and poor scalability. This chapter advocates for a shift towards human-centered participatory design (HCPD) as a pragmatic method for PPI in DHI development, emphasizing early and sustained stakeholder engagement, shared decision-making, and contextual integration. We outline key principles for effective PPI, including defining problems from patient perspectives, mapping and involving diverse stakeholders, and aligning design with implementation frameworks. A structured, stepwise approach is presented for co-designing, prototyping, deploying, and scaling DHIs while addressing common barriers such as tokenism, misalignment of stakeholder priorities, and digital literacy challenges. By embedding PPI at every stage, DHIs can be designed to enhance patient empowerment, adherence, and clinical utility. A case study of a long-running Parkinson’s disease initiative is provided to demonstrate the need for meaningful PPI in real-world settings. This chapter thus provides a practical roadmap for researchers, developers, and healthcare professionals to integrate PPI effectively, ensuring that digital health innovations are not only technologically sound but also responsive to the needs and preferences of the populations they serve.