With an expected population of 400 million by 2040, America is morphing into an economic system composed of 23 megapolitan areas that will dominate the nation's economy by midcentury. These megapolitan areas are networks of metropolitan areas sharing common economic, landscape, social, and cultural characteristics. The rise of megapolitan areas will change how America plans. For instance, in an area comparable in size to France and the low countries of the Netherlands and Belgium-considered among the world's most densely settled-America's megapolitan areas are already home to more than 2.5 times as many people. Indeed, with only 18 percent of the contiguous 48 states' land base, America's megapolitan areas are more densely settled than Europe as a whole or the United Kingdom. Megapolitan America goes into spectacular demographic, economic, and social detail in mapping the dramatic-and surprisingly optimistic-shifts ahead. It will be required reading for those interested in America's future.