For a long time, the environmentalists’ mantra was Thoreau’s declaration, “In wildness is the preservation of the world.” Increasingly, however, environmentalists have become preoccupied by the concrete jungle: the city, dressed in glass, concrete, and steel. The city’s importance can’t be over-stated, because half the world’s population now lives in urban areas, and because the city consumes for more than 75 percent of resources, worldwide. In some parts of the world cities are growing rapidly; in others they are losing population and falling into disrepair. Yet, cities everywhere are being forced to reimagine themselves due to variability in population and climate. The way they do so will have massive consequences for our communities and collective ecological resilience.