A sustainable city is a vibrant human settlement that provides ample opportunities, in harmony with the natural environment, to create dignified lives for all citizens.

Cities today are in an exciting position to take leadership on the preeminent challenge of our era: the effort to build sustainable economies. Cities are, after all, where many sustainability issues are lived out—where most commerce, energy use, production, and other modern drivers of unsustainability (and one day, of sustainability) take place.

Just as important, cities are where people are most likely to understand and engage sustainability concerns, where discussion is no longer abstract but becomes grounded and real. People care about their cities and often are motivated to protect and improve their urban homes. Cities can harness that passion to help advance a sustainability agenda, perhaps more easily than national governments or corporations can. Indeed, cities may be our best hope for shifting economies in a sustainable direction.