Firms that want to exploit Smart City's opportunities need to cooperate with local governments. From a managerial point of view, there is scant research on how to select public partners in Smart City projects. In fact, while there are several cities claiming to be ‘smart’, not all cities fulfil the essential requirements for successful Smart City projects. This paper shows how to build successful public–private alliances in Smart Cities and, more specifically, how to select the right city to test, develop or sell smart technologies. This study uses a multiple‐case research design and follows an exploratory and qualitative methodology. The results show that firms improve the success of their projects if they assess three main aspects of partner selection, these being partner complementarity, commitment and compatibility. The paper, therefore, provides several managerial implications regarding how firms may be more effective in selecting where to start their Smart City projects and how public organisations may become more attractive. Finally, academic implications, limitations and future lines of research are presented.