Smart cities use information and communication technologies to improve quality of life, efficiency of urban operation and services, and competitiveness. Several challenges result from the large use of data in smart cities; we focus here on three that we consider most urgent to address in terms of governance. The first relates to the data heterogeneity that results from the diversity of stakeholders, applications, processes and tools involved, requiring operational data governance to ensure ecosystem sustainability. The second relates to the uncertainty generated by new business models and new technologies, requiring a risk management approach that continuously takes into account new risks and threats. The third challenge is the need to adapt people's skills so that they can cope with rapidly evolving technologies.