Urban metabolism theories and concepts support the formulation of new political rationalities for urban governance. Using the case of waste management in Mexico City, this chapter explains how urban metabolism, as a conceptual framework, has become an epistemic tool to govern urban flows. The chapter looks into the application of Material Flows Analysis (MFA) within the policy context of Mexico City. The analysis focuses on how the deployment of MFA renders the urban fabric in Mexico City governable, the kind of urban relations that MFA makes visible, and the ways in which thinking about urban metabolism in this way reproduces urban inequality. We conclude that the application of MFA in Mexico City overlooks the processes of waste management that are thought of as being ungovernable. By delimitating the boundaries of MFA, and excluding outside flows, the city is characterised as a homogeneous unit and the work of informal waste handlers is rendered invisible.