The problem of Kant’s sources in Perpetual Peace has never before been dealt with in a systematic fashion. As some commentators have already noticed, Kant seldom quotes his sources in Perpetual Peace and in quite a number of other works. The purpose of the present research note is to analyze the Kantian text and to find philological traces of the various authors that we believe have been important to Kant’s work in the field of political philosophy. With this in mind, a methodology has been elaborated which includes three aspects: a textual and comparative analysis, a consistency analysis and a contextual analysis. These three approaches combined should allow us to systematically shed light on the key role played by Emer de Vattel’s famous book The Law of Nations (1758) and, more unexpectedly, by the Federalist Papers, in particular articles no 10, 14 and 51 written by Madison.