Over the past century, America changed from a nation of distinct cities separated by farmland, to a place where employment and population density is far more continuous. For some purposes, it makes sense to think of the U.S. as consisting of a number of contiguous megaregions. Using the megaregion definitions of the Regional Plan Association, this paper documents the remarkable differences between these areas in productivity, housing prices, commute times and growth rates. Moreover, over the past 20 years, the fastest growing regions have not been those with the highest income or the most attractive climates. Flexible housing supply seems to be the key determinant of regional growth. Land use regulations seem to drive housing supply and determine which regions are growing. A more regional approach to housing supply might reduce the tendency of many localities to block new construction. The Policy Research Institute for the Region at Pinceton University also provided support and funding.