This book explains why the global community has been successful in correcting some recent large-scale problems, but has failed in addressing others. The book discusses challenges drawn from the fields of global health, security, the environment, and governance. The analysis reaches from antiobiotic-resistant microbes to greenhouse gases, from civil wars to international terrorism, and from the polluted atmospheres of cities to the depths of outer space. In the process, the reader learns what ties together seemingly different problems, and what distinguishes seemingly similar concerns. The book is intended for a wide audience drawn from the social and policy sciences.