Originating in the field of manufacturing, the Digital Twin (DT) concept is now being applied across a range of application domains, from personal healthcare to whole Earth observation. Despite enthusiasm for DTs, uncertainties have arisen concerning their lack of definition and technical specificity. This paper reassesses the concept with particular consideration for its application to cities in the form of Urban Digital Twins (UDTs). Rather than identifying DTs with a particular set of technologies, we instead understand them as embodying a core ‘conceptual model’ describing a mechanism for control based on the generation and feedback of information, elsewhere characterised as a ‘steering representation’. By aligning their use with more participatory forms of governance involving the ‘commoning’ of city information, we argue that UDTs might then provide powerful new means for participation in urban planning and governance through the support they provide for communication, collective sensemaking and shared oversight.