Smart cities are increasingly advocated by governments and the private sector as the primary means to deliver urban sustainability. Particularly in Europe and North America, the smart city is envisioned as a place where digital technologies are deployed to ‘solve’ urban sustainability problems. Such visions have been broadly critiqued in the urban studies literature for reflecting techno-utopian, neoliberal approaches to urban development that exert corporate control over cities, but there has been little empirical verification of these critiques. More recently, a disparate and interdisciplinary body of literature has emerged documenting the impacts of smart city initiatives in practice. This paper provides a state-of-the-art, empirically informed analysis of smart-sustainability, which considers established critiques of smart city policy and visions alongside the increasing body of evidence concerning the actual experiences of smart city initiatives. Through a systematic review of the smart city literature pertaining to Europe and North America, we identify and test five tensions between the smart city and the goals of sustainable urban development. These tensions involve: (1) reinforcing neoliberal economic growth; (2) focusing on more affluent populations; (3) disempowering and marginalising citizens; (4) neglecting environmental protection; and, (5) failing to challenge prevailing consumerist cultures. On the basis of these findings we propose how digital technologists, urban developers, municipalities and citizens might address these tensions. A key finding is that the potential to empower and include citizens represents the key to unlocking forms of smart-sustainable urban development that emphasise environmental protection and social equity, rather than merely reinforcing neoliberal forms of urban development.