This project will develop a novel E-mental health preventive platform aimed at reducing the risk of mental illness in high-risk adolescents. Our focus on adolescence is motivated by its high social and biological dynamics, and the presence of transitions to severe mental illness during this developmental period. We will adapt an existing smartphone-based platform developed by our partner (Monsenso) to provide a tailored support for facilitating healthy behaviours and coping with psychological problems in adolescents at risk of severe mental illness (schizophrenia, bipolar disorder and major depressive disorder). We will ascertain at-risk adolescents by virtue of family history of severe mental illness or very preterm birth. We will test effectiveness of this prevention platform in a randomized control trial carried out in five countries (a total of 1,000 adolescents). Short term, we wish to create technical tools for a scalable program for mental-health promotion, and to build a related base of evidence providing insights into “what works and why”. Long term, we wish to contribute to dissemination of evidence-based tools for primary and secondary prevention of severe mental illness (and co-morbidities). This proposal will be submitted to SC1-PM-07–2017: Promoting mental health and well-being in the young.