Let us imagine a city where vehicles give off only water vapor, oil is affordable, income taxes do not exist and the economy is not based on buy ing goods any longer, but on leasing or renting them... Is this a dream? No, it is not, according to Mr. Paul Hawken. He is not only an environmentalist, entrepreneur and journalist, but also the co-author of Natural Capitalism, considered by US president Bill Clinton one of the fi ve most important books in the world. We asked him what is a Natural Capitalism and how we could build a future with the cities he describes.