A major step in our evolution occurred when we first began to organize and settle in cities. With more than half of the world’s population living in cities and all urban development since those first settlements expected to double by 2060 (UN 2011), cities are now very much the dominant habitat for our species. We are faced with a challenge to resolve our domesticated tendencies with resource and space limits of our planet. A fundamental aim of sustainability is to preserve the existence of our species; it is clear that we will need to embrace urbanism as a human quality to achieve that end. Our commitment to a global urban future demands that we move toward more sustainable urbanism. Accomplishing such a goal requires several important steps, all of which expand the fields of environmental and sustainability science and reinforce the value of considering urbanism. First, our relationship to urbanism should be expected to continue. Second, studies of cities and natural systems must recognize their inherent interdependencies. Finally, the local differences that make some cities healthier and ecologically supportive must be better understood. Each of these steps can generate broad research themes for new discovery. Recognizing our urban nature is a prerequisite.