This report is a comprehensive manual for municipal governments and their partners, city authorities, and advocates and agents of change. It invites them to address vexing and seemingly intractable problems of urban governance and to imagine future scenarios. There is little agreement on how different types of cities should aggregate, analyse and apply data to their immediate issues and strategic challenges. Yet the potential of data to help navigate cities through the unprecedented urban, climate and digital transitions ahead is very high and likely underestimated. This report offers a look at what data exists, and how cities can take the best steps to make the most of it. It provides a route into the urban data ecosystem and an overview of some of the ways to develop data policies and capabilities fit for the needs of the many different kinds of city contexts worldwide.