The aim of this paper is to improve the understanding on how city administrations can integrate ICT solutions for urban sustainability into processes of planning, i.e. how to govern the Smart Sustainable City. The paper is based on a case study of how the City of Stockholm has worked with integrating ICT solutions in the urban development project the Stockholm Royal Seaport (SRS). Through interviews with city officials and analysis of planning and policy documents we track how ICT became a part of the environmental program for the SRS, how this type of technology is conceived in terms of relation to the planning and implementation of other urban technologies, as well as what expected effects are highlighted. For this specific case we also distil some general lessons learned regarding what worked well and what did not. Finally, we draw conclusions regarding how ICT and sustainability can be merged in the planning phase of new urban developments and, ultimately, how a city administration can govern a city towards a Smart Sustainable City.