10076369ASP BelongActiveEU-FundedHorizon Europe GuaranteeIn our fast-changing society, poor mental health and social isolation are increasing among young people, exacerbated by the pandemic. Belonging – feeling connected to and accepted by others through supportive interpersonal relationships – is key to boosting mental health and overcoming loneliness. There is a lack of evidence-based interventions addressing belonging, particularly in schools, which remains a central space for adolescent socialisation. Digital technologies, while disrupting the social landscape, offer enormous potential for adolescent health management. This project develops Augmented Social Play (ASP), a pioneering digital mental health intervention format whose feasibility has been established through proof-of-concept prototype. ASP uses smartphones to deliver realworld group experiences that combine immersive storytelling, augmented reality, collaborative face-to-face gameplay and evidencebased psychotherapeutic methodologies to boost individuals’ mental health while fostering a greater sense of belonging within the group. Collaborating across academia, industry, education, health and the arts, and working with young people, we will co-develop ASP #1, a full-scale, multi-session intervention. We will implement this intervention in schools in Portugal, Czechia, and the UK, using strategies informed by policy review, and evaluate its efficacy, cost-effectiveness and implementation in order to present an evidence base to stakeholdersincluding policy-makers, practitioners and media,stimulating wide uptake. We will further evolve ASP by collaborating with vulnerable adolescents to ensure we meet the widest spectrum of needs; by prototyping additional ASP interventions aimed at different populations and threats to mental health; and by creating comprehensive ethical guidelines. Our long-term goal is wide-scale adoption of ASP, making multiple smartphone-delivered group mental health interventions freely accessible to diverse populations and settings.