In this article, I defend the idea that Bentham's international political theory entails a cosmopolitan dimension. First, I explain that Bentham rejects two pillars of internationalism, namely, the sovereign's unconstrained autonomous power and authority in international politics, and the legal and moral personality of the state in the international realm. This critique leads Bentham to construct a complex international political theory which places the issue of states’ responsibility at its centre. Bentham's international theory articulates a minimalist international system of cooperation between states (Part II) and an institutional model of public officials’ responsibilities that together play the crucial role in securing the greatest happiness of the greatest number in the world (Part III). In this last part, I explain how Bentham's international political theory relies heavily on the responsibilities of states, a set of responsibilities that encompasses both national and cosmopolitan responsibilities that public officials in each state hold.