Ours is the century of cities. Already by 2010, 50.5 percent of the world’s population was living in urban areas. In a few decades that number will rise to 70 percent. During the 21st century, the world as we know it will be defined by the tempo, geography and challenges of city life. Cities will be hubs of commerce, culture and technology. This is not entirely new to world history. Going back to medieval burghers of northern Europe and grand cities of China, India and the early Islamic empires, cities have been where culture and innovation have shaped civilization. But the pace and manner in which the realities of city life will define politics, economics, global relations, climate change, energy consumption and integration of our world into one shared global reality is new. It represents the next frontier in human development.