To be a cosmopolitan—i.e., a citizen of the world first and only secondarily a member of a particular nation—is an ideal that has a long history. It dates back to the ancient Greek philosopher Diogenes of Sinope in the third century BCE. If someone asked him where he came from, he would only reply, "I am a citizen of the world." In this overview of the cosmopolitan ideal, philosopher Peter Kemp argues that in the twenty-first century cosmopolitanism is more relevant than ever before. In fact, he insists that it is the only viable guiding ideal for politics and education in an increasingly interdependent world. Kemp begins with an analysis of our current situation. Financial globalization, intercultural coexistence, and our joint responsibility to sustain world resources and preserve the climate are significant, unprecedented challenges that call for a cosmopolitan perspective. Small groups of individuals or nations cannot manage these problems alone. He next traces the history of the cosmopolitan ideal from the Stoic philosophers of the classical period through the development of canon law in Christian medieval Europe to the Enlightenment of Immanuel Kant, who infused his legal philosophy with a cosmopolitan viewpoint. Kemp concludes with a thorough analysis of the tasks of our contemporary era. To tackle our enormous common problems today, we need new ideas about learning and cultivation in order to enhance a cosmopolitan ideal in both education and politics.