The 21st century will be urban; more than half of the world population will be living in one city in 2030 against only 10% back in 1900.

But the city of 2030 will not resemble to the 20th century one : increasingly spread out and multipolar, varied and fragmented, penetrated by networks and inserted in the world exchange system, autonomous towards the Nation-States, concerned by its «ecological impact» and also the social tensions in its center, this city is deeply reinvented. Technologies play an important role in this change as for the help of the town citizens in order to organize complicated webs in their relations, their occupations and their travelling; to further a more flexible production and distribution in real time and connected to multiple networks; to organize the exchange between citizens with or sometimes against the city institutions.

Today, the cities function and grow as living bodies; it is difficult to plan their development or at least to meet reality with programs. One could issue construction rules, a plan, infrastructures, but not the effective distribution of activities, the living style, the places where public reel spaces are located in which people have pleasure meeting each others, the effective arrangement of transportation methods… The cities are intrinsically plural: many types of population mix along and many uses come out of there, many private, public and associative actors deploy their activities and compete… These uses, practices and relations are in constant change: would the lasting city turn to a dynamic city by the economic growth, a city of pleasure and creation? How to win the frugality in resources, the master of rejection, the awareness of global effects for each action, the solidarity, with all the characteristics that are behind the attractiveness and the competitiveness of a city? How to reach public decisions, difficult arbitration necessary to progress to a « lasting » mode of development? The challenge that awaits the new urban planners is to plan the unpredictable: how to create « parameters » (essential infrastructures, rules of town planning) in order to direct the development of the city without a priori compelling it? How to imaging buildings or spaces entirely reshaped by using them? How to adjust an urban politic around confirmed and shared objectives, without necessarily having to manage details in a centralized manner? Today, it is one of the biggest challenges of « urban government » that spread out: a matter of democratic engineering as well as a matter of design, town planning and infrastructures. At this condition only, the « lasting city » will spread out beyond all plans and intentions.