This chapter argues that Giuseppe Mazzini's thought belongs to the tradition of cosmopolitanism insofar as he deems the self-determination of autonomous and democratic nations the precondition for a peaceful international order. Countering the nationalistic interpretation of his thought, and Giovanni Gentile's reading in particular, it maintains that Mazzini, whose political education occurred in the aftermath of the collapse of Napoleon's empire, believed that the individual (as a primary good and the recipient of equal rights) and the nation (as the collective sovereign that has the power of giving individual rights a legal status) were the two modern agents of political and moral resistance against imperial projects. Beginning with the Abbé de Saint–Pierre, Kant, and the Saint–Simonians, the pact of union and the association of autonomous nations became, in a kind of federative covenant of mutual help and cooperation, the language of European democrats and republicans. In the 20th century it was adopted by those jurists who deemed the consolidation of the rule of law and constitutional democracy intermediary and necessary steps towards a global legal order. Mazzini must be interpreted as belonging to this tradition, though in a peculiar way since he was a cosmopolitan not despite, but because of, his advocacy of the principle of nationality.