It is widely assumed that the ¿dense vertical city¿ is more sustainable than the ¿dispersed horizontal city.¿ This concept has certainly been a large factor in the unprecedented increase in the construction of tall buildings globally over the last few decades, especially in the developing world. The concentration of people in denser cities ¿ sharing space, infrastructure, and facilities ¿ is typically thought to offer much greater energy efficiency than the expanded horizontal city, which requires more land use, as well as a higher energy expenditure in infrastructure and mobility.Though this belief in the sustainability benefits of `dense¿ versus `dispersed¿ living is driving the development of cities worldwide, the principle has rarely been examined at a detailed, quantitative level. Studies to date have been mostly based on large data sets of generalized data regarding urban-scale energy consumption, or large-scale transport patterns. Crucially, there are very few studies that also consider a ¿quality of life¿ aspect to urban vs. suburban living, in addition to differences in energy use patterns.Chicago, subject city of the research, is uniquely positioned for a study exploring density vs. sprawl from a sustainability point of view. The birthplace of, and center for innovation in tall buildings, Chicago also has an ever-growing suburban area that is typical of most US cities. And yet, again in line with many other cities around the world over the past decade or two, it has seen suburban growth alongside densification of its downtown area and a resurgence of people seeking high-rise urban living.This research report offers a quantitative evaluation of long-held assumptions, and with sometimes surprising results. The ground-breaking study quantitatively investigates and compares the sustainability of people¿s lifestyles in both urban and suburban areas from environmental and social perspectives, using detailed information directly collected from households and best