In constitutional States, principles are of different kinds. Some are of procedural nature or point to the functioning of law (‘how’), some others encapsulate the raison d’etre, purpose and value (‘what’ and ‘why’) of the legal order, as a whole. With regard to the International legal system the second kind of principles remains much disputed upon, although a clarification of such an issue would be of relevance in the development of IL, especially in the adjudicative sphere. One of the obstacles to overcome is certainly the account and narrative that legal positivism has offered of IL. This article shall explain, on the one hand, some weaknesses of traditional positivism, with particular concern for the transformation and interweaving of legalities in the supranational sphere. On the other hand, it shall appraise especially the contribution by the late Ronald Dworkin to IL, and how his interpretive theory of law can be projected onto the international environment. Eventually, recent cases before international Courts shall be considered, that expose the way judicial reasoning actually profits from asking questions of principles.