As more and more people leave villages and farms to live in cities, urban growth results. According to the UN State of the World Population 2007 report, sometime in the middle of 2007, the number of people living in cities and towns has overtook the number of people living in the rural areas and this event was recorded in the history as the arrival of the "Urban Millennium" or the 'tipping point'. In regard to future trends, it is estimated 93% of urban growth will occur in developing nations, with 80% of urban growth occurring in Asia and Africa. Urged by these observations, city halls and political decision makers have become very alert, calling for urgent solutions to the growing problems. However, the recent advances in information and communication technologies may stimulate new solutions towards the urbanization problems. This is verified as a target research and innovation area in Horizon 2020 of European Union Policy under the challenge 'Secure Clean and Efficient Energy' with the main goal of jointly Smart Sustainable Cities. The aim is to integrate and validate ICT technologies and services in neighbourhoods to make progress towards intelligent cities by exploiting ubiquitous technologies. In addition to technical developments, attention is given to innovative service business models which include security, safety and privacy issues. Our need to improve our understanding of cities, however, is pressed not only by the social relevance of urban environments, but also by the availability of new strategies for city-scale interventions that are enabled by emerging technologies. Leveraging advances in data analysis, sensor technologies, and urban experiments, City Science will provide new insights into creating a data-driven approach to urban design and planning. To build the cities that the world needs, we need a scientific understanding of cities that considers our built environments and the people who inhabit them.