Transforming a city into a Smart City is a complex and multidimensional process which changes over time since all the involved stakeholders work to achieve more and better results. “To be smart” affects many aspects of a city including economics, government, people, living, mobility, environment, energy and services. This paper aims at critically analysing the main features related to smart cities such as terminological issues, the heterogeneous theoretical background and the methodological limits of the few existing measurement experiences.