Van Gend en Loos (VGL) established the conceptual premises of a crucial issue to shape the relationships between the European Union and international law: the function of direct effect as a powerful instrument to guarantee that the rules of one system are complied with in another legal order. However, if compared with direct effect of EU legal rules, the issue of the effects of EU international agreements is made more complicated by the combination of the more traditional question of the self-executing character of international agreement provisions and the narrow meaning of direct effect. The former issue, strongly affected by the technique of incorporation and the rank of international law obligations within the incorporating legal order, goes to the heart of the constitutional architecture of the EU legal order where a balance is to be found between the obligation to comply with international law and the integrity of the EU legal order. The latter notion concerns instead the relationship between the private person and the legal rule and defines the special character of the EU which distinguishes it from international law. Since such a quality of EU rules cannot be automatically applied to international law rules incorporated in the EU legal order it must be verified case by case. This is the reason why, for the present author, the double test approach, first applied by the ECJ in VGL, is the right test to determine direct effect of EU international agreements, but cannot be applied to verify the self-executing effect of international law in the traditional (broader) meaning.