Circular economy (CE) principles can be applied at different scales: from materials to products, from individual supply chains to industries, from cities to national and transnational economies. In order to design a CE at any scale, a system approach is needed to describe and analyse the current situation and to model and implement the transformations required. In this paper we show how Urban Metabolism (UM) research can support the design of CE in cities. Urban metabolism considers resource consumption and environmental pressure of urban areas in a systemic way. The Urban Metabolism Group at Chalmers is developing three alleys of research: UM description, analysis and sustainable UM design. Findings from each of these may inform CE design by for example: quantifying resource flows at the product and material levels and with respect to industries and other sectors using them; identifying possible links between stakeholders with suitable materials and infrastructures; connecting material flows with life cycle impacts for multidimensional priority setting; depicting the drivers of material flows; and modelling policy effects on material flows. In this way, urban metabolism research can provide a comprehensive framework to investigate the pathways to circularity at both the urban and regional level.