Recently, British Prime Minister Theresa May made a bold anti-cosmopolitan claim: ĎIf you believe you are a citizen of the world, you are a citizen of nowhere. You donít understand what citizenship meansí. Given that many have never found nationalism particularly appealing, some have been moved to become citizens of the world after hearing these lines. But how is one to become a cosmopolitan? The answer is found in the history of philosophy. Cosmopolitanism has taken many forms. There are moral, political, legal, economic and cultural cosmopolitanisms. A form that has not received much attention is therapeutic cosmopolitanism. The focus of this form is on how being a world-citizen entails certain health benefits. I argue that therapeutic cosmopolitanism is both the original and best way of being a world-citizen. To do so, I summarize the present taxonomy of cosmopolitanisms and show how therapeutic cosmopolitanism contrasts with these options. I use classical Cynicism as the primary example of therapeutic cosmopolitanism. Instead of the universalist humanism and supranational communitarianism that characterizes cosmopolitan options, Cynic cosmopolitanism employs extreme naturalism. I show how being a Cynic cosmopolitan is the preferable way of rejecting nationalists of all stripes.