old industrial cities like Detroit have continued to decline, while others like Boston have rebounded. From its founding, Boston emphasized education, which helped the city reinvent itself several times: as a trading port with the West Indies and Europe in the 17th century; as a manufacturing center in the 1850s; and as a financial, biotechnology, and hi-tech center a century later. New York is another example of a city that has recently made a successful transition based on human capital, replacing shipping, manufacturing, and the garment industry with global finance.

While urban failure is dismally similar—high poverty rates, abandoned buildings, decaying infrastructure—success takes many forms, which is why Los Angeles, London, and Singapore are physically so different. In fact, some of the most creative urbanized areas in the UnitedStates—Silicon Valley and Boston's Route 128—don't look like traditional cities at all. Neither does Houston (the nation's fourth-largest city) which, Glaeser compellingly argues, offers middle-income Americans something missing in more glamorous cities: jobs and affordable housing.

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Glaeser defines the city as a "mass of connected humanity." His emphasis on human capital is important because politicians and planners tend to overvalue the physical environment. They encourage cities to look for the Next New Thing, whether it's pedestrian malls, downtown stadiums, iconic museums, or light rail. It is as if 13th-century European cities, envious of Venice's great commercial success, had said "Oh, that's the trick—we just have to turn our streets into canals." The conflict between people and places is currently playing out in the plans to rebuild New Orleans after