How do we build the city of tomorrow? One that combines the benefits of the countryside with the advantages of the urban world? Manon and François, two young city dwellers, traveled between Mexico, Europe, and the US in search of concrete and revolutionary initiatives at every scale that bring nature back to the heart of cities. Accompanied by associations, business leaders, and city experts, they provide inspiring ideas to propel cities into the 21st Century: from revegetation to urban farming and bio-waste recovery. By making the link between all these solutions, they offer us their vision of what the green city of tomorrow could be, calling on government, private companies, and citizens to take action.