Rapid urbanization is the dominant demographic trend in the 21st century. Urban design must focus on optimizing natural resources and human health. When building and managing cities, it must be a priority to reduce the overall ecological footprints by reducing impacts on biodiversity; air and water pollution; and per capita energy, water, and arable land use. Designing highly efficient cities and simultaneously capitalizing on health co-benefits, such as cleaner air and using physical activity as transportation, could make an enormous positive impact on health. Further research is needed to develop principles of effective sustainable urban design that promote the physical and mental health of urban dwellers while reducing the global ecological footprint of the world's cities.