How to achieve low carbon goals and fight against global warming? How to feed the nine billion human beings who will soon share the planet and its increasingly limited resources? How to house them? How will the cities of the 21st century win the challenge of the energy transition? Architect Vincent Callebaut and his teams offer eco-responsible solutions to these crucial questions. This is the state of mind, the “state of action” in which they invent new ways of living. Their projects take place in the cities of tomorrow, metabolic, creative and fertile. The facades become skin; they are intelligent, regenerative and organic. Their roofs are the new floors of the green city. Their gardens are not next to the building, they are the building! Architecture is transformed into cultivation, food. All waste is recycled, thus inventing a new circular economy. The projects presented in this conference are actual manifestos that advocate bringing nature and the countryside back into the city. Not a cosmetic nature that conceals buildings just to make them beautiful, but a proactive nature, which transforms our energy hungry cities into nourishing biotopes and their citizens into gardeners. Just as Vincent Callebaut announces: “Transforming our cities into ecosystems, our neighbourhoods into forests and our buildings into inhabited trees: this is our credo!”