The project aims at supporting urban transformation processes towards the circular economy by making an inventory of the existing material stocks within urban construction, developing reliable scenarios for future expected material flows, and providing governance arrangements on how to approach the circular economy transition. The project will focus on the largest urban infrastructures and communal assets, namely buildings, municipal roads, water, and wastewater pipes. A truly transdisciplinary consortium will work with a mixed research design that integrates quantitative modelling with qualitative study and design of governance aspects. The project will further improve already existing, validated, and applied tools and arrangements and combine them with new digitalization technologies to inform decision-makers and enable a circular built environment. This will be achieved by engaging with a wide range of stakeholders in a co-creation process with three urban living labs and six fellow cities in five countries, which will result in numerous capacity building moments throughout the entire project. A thorough analysis of best practices of cities steering the circular economy transition together with new governance interventions will result in concrete proposals of tailored governance arrangements for the participating cities including a concrete proposal for an upscaling strategy for Europe.