The concept of urban metabolism, referring to the exchange processes that produce the urban environment, has inspired new ways of thinking about how cities can be made sustainable and has also raised criticisms about the specific social and economic arrangements in which some forms of flow are prioritized or marginalized within the city. This article explores how the concept of urban metabolism travels across disciplines, using a comparative analysis of different approaches to urban metabolism within industrial ecology, urban ecology, ecological economics, political economy and political ecology. The analysis reveals six main themes emerging within interdisciplinary boundaries in relation to urban metabolism, and how this concept enables new understandings of (1) the city as an ecosystem, (2) material and energy flows within the city, (3) economic-material relations within the city, (4) economic drivers of rural-urban relationships, (5) the reproduction of urban inequality, and (6) attempts at resignifying the city through new visions of socioecological relationships. The article suggests potential areas for cross-disciplinary synergies around the concept of urban metabolism and opens up avenues for industrial ecology to engage with the politics and the governance of urban development by examining the city and its metabolism. © 2012 by Yale University.