The field of political demography—the politics of population change—is dramatically underrepresented in political science. At a time when demographic changes—aging in the rich world, youth bulges in the developing world, ethnic and religious shifts, migration, and urbanization—are waxing as never before, this neglect is especially glaring and starkly contrasts with the enormous interest coming from policymakers and the media. “Ten years ago, [demography] was hardly on the radar screen,” remarks Richard Jackson and Neil Howe of the Center for Strategic and International Studies, two contributors to this volume. “Today,” they continue, “it dominates almost any discussion of America’s long-term fiscal, economic, or foreign-policy direction.” Demography is the most predictable of the social sciences: children born in the last five years will be the new workers, voters, soldiers, and potential insurgents of 2025 and the political elites of the 2050s. Whether in the West or the developing world, political scientists urgently need to understand the tectonics of demography in order to grasp the full context of today’s political developments. This book begins to fill the gap from a global and historical perspective and with the hope that scholars and policymakers will take its insights on board to develop enlightened policies for our collective future.