The CITYkeys project will adresses the horizontal challenges: The current transition to low carbon, resource-efficient cities is moving slowly. Innovative and smart solutions are available but uptake in other cities is low, because the impacts of the smart city solutions are not objectively verified and because of lack of confidence that the solutions can also be applied in other contexts and cities. This project aims to speed up the transition by facilitating and enabling stakeholders in projects or cities to learn from each other, create trust in solutions, and monitor progress, by means of a common performance measurement framework.