History has taught us that urbanization and economic development go hand in hand. But the experience of developing world nations today has been more mixed. In some oft-cited cases like the booming regions around Beijing and Shanghai, city growth has been associated with rapid economic development. And throughout the developing world, cities have far higher levels of economic productivity when compared to their nations as a whole. But in many other cases, urbanization has been accompanied by low levels of economic growth -- a phenomenon that Harvard economist Edward Glaeser has called "poor country urbanization."