Smart cities focus on using existing resources in a better way to improve the urban environment. At the same time Big and Open Linked Data (BOLD) can be used to better understand the use of the resources and to suggest improvements. The objective of this paper is to investigate the complementariness of the smart cities and big and Open Data research streams. Two inductive cases concerning different aspects of smart cities, energy and mobility, are investigated. The idea of using BOLD for smart cities seems initially straightforward, but the cases show that this is complex. A taxonomy for forms of collecting and opening data is derived. A major challenge is to deal with data distributed over various data sources and how to align the data push with the citizens’ needs. This paper highlights a continuous scale between open and closed data and emphasizes that not only Open Data but also closed data should be used to identify improvements. BOLD can contribute to the ‘smartness’ of cities by linking and combining data or employing data or predictive analytics to improve better use of resources. A smart city only becomes smart when there are smart citizens, businesses, civil servants and other stakeholders.