We cannot approach cities in the same ways we address airplanes, factories, and power plants. Cities are laced with too many complex behavioral and social phenomena. Yet we can systematically explore the ways in which cities might respond to opportunities, incentives, and inhibitions. We can then identify the conditions more likely to lead to one response rather than another. Then we can think about how we might engender the conditions leading to more appealing responses. Our focus is on how to get a city to design itself in ways that improve the quality of life for everyone.