Over the next two decades, the world will see a burst of urban expansion at a speed and on a scale never before witnessed in human history. But not all the world will take part. When you hear about the coming urban age, it's really a story about rising Asia and the two countries that will define this new era of the megacity: China and India. Half of Asia will become urbanized, and nearly a billion people will shift from countryside to cityscape. Trillions of dollars will need to be spent on roads, trains, power plants, water systems, and social services. And it's going to happen in less than half the time that it took the West. China and India will account for two-fifths of the world's urban growth, but they are pursuing wildly different strategies for managing this shift. Beijing's approach is systematic: The government has invested ahead, allocated land, plotted out transportation networks, and given its cities the freedom to raise capital. New Delhi, meanwhile, hasn't done enough to prepare. So while China has embraced a future of office parks and high-speed rail, India is just waking up to its new urban reality.