Over 70% of the population in industrialized nations live in cities; in the next decade so will most of the world's entire population. This volume examines the impact of urban living on human health and biology. Cities pose numerous and diverse social and biological challenges to human populations. These challenges bear little resemblance to the forces that molded human biology throughout millions of years of evolution. Urban populations in industrialized nations have distinctive patterns of behavior, social stratification, stress, infectious disease, diet, activity, and exposure to pollutants from years of industrialization. These features affect diverse aspects of human function including human nutrition, energy expenditure, growth, and reproduction.