We consider how data is produced and used in cities. We draw on our experiences working with city authorities, along with twenty interviews across four cities to understand the role that data plays in city government. Following the development and deployment of innovative data-driven technology projects in the cities, we look in particular at collaborations around open and crowdsourced data, issues with the politicisation of data, and problems in innovating within the highly regulated public sphere. We discuss what this means for cities, citizens, innovators, and for visions of big data in the smart city as a whole.