Unfortunately, the future of cities is still not much in the political debate. However, it is in cities that part of the destiny of humanity will be played out: more than half of the population of our planet (i.e. approximately three billion people) is now made up of city dwellers. In France, more than 80% of the population now lives in an urban area. Although they occupy only 2% of the world's territory, they account for 75% of greenhouse gas emissions, calling into question traditional economic development models. In thirty years' time, five billion of us will be living in large megacities and urban areas with more than ten million inhabitants.