‘I speak ... as a fellow citizen of the world’ (Obama, 2008). These were the words used by Barack Obama in Berlin in July 2008 during his first presidential campaign. If he explicitly echoed another very well-known assertion, that of President Kennedy ‘Ich bin ein Berliner,’ Obama seems here a cosmopolitan candidate. This interpretation relies not only on his own life, which is, to a certain extent, cosmopolitan; his father was Kenyan and he spent part of his childhood in Indonesia. He also elaborates his speeches by referring to this cosmopolitan tradition of thought (Hammack, 2010). In fact, his election generated hope not only in the United States but also in the rest of the world. This first black man who accessed to the highest political responsibility of the country embodies a cosmopolitan president. Peoples felt that his presidency would be as beneficial to Americans as to the nationals of other countries. The Nobel Peace Prize he received shortly after his enthronement strengthened such feeling. Indeed, Barack Obama would be a Kantian in the Oval Office (Selzer, 2010). This episode illustrates the link between hegemony and cosmopolitanism. The two do not seem antithetical. Such a link directly echoes the concept used for the first time in the history of political ideas. In the Peloponnesian War, Thucydides distinguishes between arkhe (control and domination) and hegemonia (legitimated leadership). While the first is based on instruments of coercion, the second means responsibility. In other words, hegemony differs from an imposed order or force but refers to the protection and recognition of others. The term is used to describe Sparta (and not Athens) by the Corinthians, who complain of being threatened by the Athenians. They call to the Spartans for help and, more fundamentally, ask them to secure their hegemony by protecting their allies. This idea of hegemony is applied at the individual level. For the Stoics, a hegemonic human being is a person responsible for himself. Hegemonism may be deformed and in this case, human beings deny themselves, deny others and their existence. The purpose of this chapter is to discuss this thesis and, more specifically, to show the limits of a virtuous link between hegemony (and a fortiori hegemonism) on one hand and cosmopolitanism on the other. The competition for hegemony specifically prevents a cosmopolitization of states. But this competition differs from the classic military struggle. We must point out that cosmopolitanisms are not uniform, but have different shades. They nonetheless refer to the same idea that the world relies on a legal or even political unification. In this chapter, I will use the Kantian model as the most important cosmopolitan source. After having specified the nature of relations between hegemony and cosmopolitanism in the theory of international relations (both scientific and normative), I will analyze a double dimension of this competition in the contemporary context. The first is located on the strategic level, the second has a normative aspect.