This paper presents a review of the state-of-the-art in Smart Cities describing the trends in different aspects, reviewing recent technologies and showing various successful projects that have been implemented in different cities worldwide. Since the introduction of the Internet of Things (IoT) paradigm, among the multiple application areas identified in literature, the implementation of IoT paradigm in the urban context has been one of the most attractive, defining the so-called Smart City concept. The objective of this work is to have a first approximation of the overall aspects of a Smart City and how IoT technologies can be viewed as catalyst in the economic, social, cultural and governance transformation process of a conventional city.