To this day, many techniques, tools and approaches have been developed and tested either on a lab scale or in pilot buildings around Europe. These demonstrations have served as great showcases for circular built environments, but they are yet to be demonstrated at higher level. Copenhagen, Hamburg, Helsinki region (City of Vantaa) and Greater London have teamed up with partners from the entire built environment value chain. The results will have a direct uptake in the value chain and enable cities to initiate circular transition. CIRCuIT will demonstrate three innovative solutions in the four cities: dismantle buildings to reuse materials; transformation and refurbishment; and design for disassembly and flexible construction. CIRCuIT will develop urban planning instruments to support cities in implementing circular construction solutions and initiate changes at system level; implement a Circularity Hub, a data platform to evaluate progress of circular economy and regenerative capacity; and set up a knowledge sharing structure, the CIRCuIT Academy, to promote upscaling of solutions. London, Hamburg, Helsinki region and Copenhagen have the ambition to bridge the implementation gap from individual pilots to the actual circular and regenerative city, by demonstrating the application of current and future developed tools and instruments for circular built environment at a city level in 36 demonstration projects. It is the intention to boost the regenerative capacity of the three cities and Helsinki region, and finalise the development of an advanced set of indicators for impact measurement in an effective and cross-European monitoring programme. The aim is to increase the regenerative capacity in the four cities, and to reduce the yearly consumption of virgin raw material by 20% in new built environments, and to show cost savings of 15%.