This paper considers the limits and potential of ‘urban metabolism’ to conceptualize city processes. Three ‘ecologies’ of urban metabolism have emerged. Each privileges a particular dimension of urban space, shaped by epistemology, politics, and model-making. Marxist ecologies theorize urban metabolism as hybridized socio-natures that (re)produce uneven outcomes; industrial ecology, as stocks and flows of materials and energy; and urban ecology, as complex socio-ecological systems. We demarcate these scholarly islands through bibliometric analysis and literature review, and draw on cross-domain mapping theory to unveil how the metaphor has become stagnant in each. To reinvigorate this research, the paper proposes the development of political–industrial ecology, using urban metabolism as a boundary metaphor.