Suárez and Grotius, the law of nations is applicable to an extra-national domain and inarguably becomes positive law. Yet, it also contains an ethical element that prevents it from transforming into a mere reflection of state interests. This work argues that this resemblance is hardly a coincidence: Grotius has read Suárez, and that influence has modified the foundations of his early thoughts on jus gentium. This should not be taken to imply that the Dutch jurist wasn't original: in both authors, the definition of the law of nations pursues his own internal logic. Nevertheless, Suárez's oeuvre allowed Grotius to solve a fundamental problem touched on in his early writings that had remained unanswered. Accordingly, his oeuvre promises to clarify one of the most significant moments in the History of International Law.