A new era is here: welcome to Planet City. The end of 2008 marked a significant shift in the history of humanity - we are now a predominantly urban-living species. Today, every modern metropolis must respond to a fundamental question: how can nature play a central role in their development, which is both ecological and sustainable, and which allows humans to live in harmony, like in an ecosystem? New York, Tokyo, Rio de Janeiro and Paris are pioneers. Each city is a giant laboratory, experimenting and developing urban ecology, according to its own natural history. Through their investigations, scientists, artists, architects and naturalists will find themselves at the forefront of these major technological and architectural challenges. Their aim is to create a synergy between city and nature, and work on the process of developing the ingredients for tomorrow?s world.