This paper presents the findings of an interdisciplinary academic exchange exploring the transition towards a circular built environment (CBE), developed over two years of collaborative work at Delft University of Technology’s Circular Built Environment Hub. A key outcome of this work is developing a comprehensive definition of the CBE and the related Scales to Aspects model, which connects the multi-scalar and cross-disciplinary nature of circularity, ranging from materials and components to buildings, neighbourhoods, cities, and regions. It highlights critical tensions, such as the lack of integration between circular strategies and other global challenges.