Part 5: Smart Cities ; International audience ; The transition of our society towards a sustainable, low-carbon reality is challenging governments at all levels to establish, implement and monitor policies that can realize this transition. In the Netherlands, cities are developing data-driven policies to ensure that the urban environment will make the transition from the use of natural gas to sustainable alternatives. However, the collection and (re-)use of data is not without its challenges, which may hamper policymaking, and thereby the ambitions for the transition. Therefore, this paper explores barriers to the data collection and use for the urban heat transition, based on literature and practice. First, an overview of barriers is derived from literature. Subsequently, we interview policy makers of eight frontrunner cities to explore which barriers they encounter in practice. We find that cities need different data in different phases of the strategy development, and that the main barriers for the collection and re-use of data are the required amount of effort and time, and the experienced difficulties to take decisions based on data that is poor in quality, level of detail and topicality.