Research on the circular built environment has to date focussed mainly on technical aspects of circularity in the built environment, emphasising the development of methods, tools, and frameworks to facilitate technical solutions that can narrow, slow, close, and regenerate materials cycles. Despite progress made in understanding the technical possibilities of circularity in the built environment, and although there has been longstanding acknowledgement that new forms of inter- and transdisciplinary collaboration are needed to accelerate and scale up solutions for the circular built environment, studies have also consistently highlighted the lack of collaboration as a significant barrier. In this position paper, we argue that existing research tends to focus on collaboration at the level of the building project, and this neglect calls for developing longer-term collaboration for circularity as a multi-level transition that considers the interactions between multiple parties involved in extended and multiple product lifecycles traversing multiple scales beyond the building project.@en