Childhood and adolescent obesity is a major global and European public health problem. Currently, public actions are detached from local needs, mostly including indiscriminate blanket policies and single-element strategies, limiting their efficacy and effectiveness. The need for community-targeted actions has long been obvious, but the lack of monitoring and evaluation framework and the methodological inability to objectively quantify the local community characteristics, in a reasonable timeframe, has hindered that. Fortunately, technological achievements in mobile and wearable electronics and Big Data infrastructures allow the engagement of European citizens in the data collection process, allowing us to reshape policies at a regional, national and European level. In BigO, that will be facilitated through the development of a platform, allowing the quantification of behavioural community patterns through Big Data provided by wearables and eHealth- devices. During the project, BigO will reach out to more than 25.000 school and age-matched obese children and adolescents as sources for community data. Comprehensive models of the obesity prevalence dependence matrix will be created, allowing, for the first time the data-driven effectiveness predictions about specific policies on a community and the real-time monitoring of the population response, supported by powerful real-time data visualisations. In short, BigO will provide an innovative new suite, allowing the Public Health Authorities to evaluate their communities based on their obesity prevalence risk and to take local action, based on objective evidence. BigO does not aim to redefine, from the ground-up, the existing obesity-related policy strategies targeting childhood obesity prevalence. BigO does, however, aim to redefine the way those strategies are designed and deployed in the European societies.