The concept of Smart City is considered increasingly strategic for the solution to the questions related to the irreversible urban agglomeration growth. Created in the nineties in parallel to the liberalisation process of telecommunications and the development of internet services, this expression risks remaining too generic and without a shared operational definition. This paper contribute to the existing literature in two ways: i) providing an overall survey of the definition and measurement problems; ii) deriving some methodological suggestions from the analysis, in order to proceed towards a robust and comparable Smart City measurement system. The latter results extremely relevant in the perspective of a dedicated monitoring system implementation.