Cities are now the main Biotope of Man, they consume spaces increasingly important, are very artificial and leave little space for nature. In an environmental concern and due to the lack felt and expressed by citizens, territorial actors implement new policies, strategies to reintegrate nature in the heart of cities. The interest is twofold: environmental (global warming, the fight against pollution) and societal (city too mineral, strong demand for recreational space kind). How to reconcile these stakes, the pressure of the actors and the population? In this study, two local policies major French Metropolis that we will study, try to understand, dissect and criticize: the Metropolis of Lille and Lyon. Both cities have implemented a policy ...