In 2000, hourly wages of prime-age men were 31% higher in metropolitan areas of over 2.5 million people than those of less than 100,000 people. Moreover, the relationship between wages and population monotonically increases by about 1 percentage point for each additional 100,000 in population over the full range of metropolitan area size. The existence of this city-size wage gap implies that workers are more productive in larger cities. Since 1980, a strong positive monotonic relationship between city size and wage inequality has also emerged.  The investigators have designed a research program to improve understanding of the roles of city size in generating gaps in worker productivity, wages, and wage inequality.