This paper explains how the city operates as a vehicle for the politicization of undocumented immigrants. I introduce a theoretical understanding of ‘liminal politics’ that focuses on the symbolic and spatial practices whereby the undocumented, who find themselves between and betwixt statuses, enact and perform citizenship. Based on a multi-sited ethnography of undocumented activism in Chicago and Brussels, I show how such a liminal politics relies on urban space in two ways: first, by its dependence on safe spaces wherein the undocumented can (re-)imagine themselves as citizens and second, by its use of public space as a theatrical stage to express rights-claims. This study thus shows that urban space is a crucial political resource for relatively marginalized populations’ struggles over citizenship.