In the new urban thinking, "economic possibility" evolves into "ecological necessity". Planning projects can no longer be satisfied with the creation of "forms and spaces" but must now concern themselves with the relations between natural processes and human activities. American culture is city-based. The urban landscape (with clustered skyscrapers) plays a leading role in its collective imagination. A majority of Americans today live in cities. In absolute numbers, the United States actually has the world’s third largest urban population. More than thirty percent of Americans live in cities of more than five million inhabitants. These urban centres represent a formidable force on national and global economics. After decades of thinking of the city as gridded and mineral-based, dedicated to the car and the service sector, to efficiency and to "progress", today urban societies find themselves at the centre of an interesting shift: one transforming the values of economy into the values of ecology. Our planning and architectural languages will, from here on, account for these changes. New projects will need to demonstrate a superior flexibility in order to stretch wide between form and usage. A new urbanism will have biological and climactic objectives. It will benefit from advanced studies on complex natural and vital systems to help reorganize failed urban territories.