A new tendency is on the rise in EU urban policy-making: adopting Co-production Arrangements inspired by the paradigm of the Commons (CAC). Some pioneering cases stand out, such as the Urban Commons Regulation in Bologna (2014), the Commons Transition Plan in Ghent (2017) and the Citizen Assets Programme in Barcelona (2017). These cities have been joined by others that either have adopted similar arrangements or are currently considering adopting them. By and large, these arrangements aim to redistribute decision-making power to citizens over services and resources that are considered as essential for urban collective wellbeing (e.g. public buildings and spaces, energy and water utilities) by fostering community self-management. Preliminary and applied research on these arrangements has been carried out, mostly based on single case study analyses. However, scientific, in-depth and comparative knowledge on CAC is still scarce. By adopting an urban epistemology to the traditional state-centred political science field, COMMONCITY will produce key, useful and timely knowledge on CAC. It will comparatively analyse the i) policy models, ii) political, social and administrative challenges, iii) impact on urban democracy of recently adopted CAC in the three EU pioneering cities: Barcelona, Bologna and Ghent. By adopting a co-production-oriented approach to data collection and analysis that will foster citizen science, it will provide unique empirical data on the varieties, effective functioning and democratising effect of these arrangements. The results of COMMONCITY will contribute to the scientific debate in the broad urban study field and, specifically, in urban democracy, urban governance, urban policy-making and urban participation. It will also provide policy recommendations to various levels of government, in order to foster the adoption of CAC and improve the functioning and democratic impact of existing and under-adoption ones.