The philosophy of EU law builds upon the philosophy of law in general and the philosophy of the EU in general. It enriches, and is enriched by, our understanding of both. In particular, the philosophy of EU law tracks and examines the intersection of four core legal philosophical questions in light of the peculiarities of the EU. First, there is the overall justification of the authority of the EU legal order, and of the EU as a socio-political project more generally. Secondly, the inquiry addresses the deep normative orientation and interpretive grain of EU law. Thirdly, it asks how EU law operates as a valid and effective framework of practical reasoning. How does EU law work as law? And finally, questions of the integrity or coherence of EU law, in particular its relationship, both continuous and discontinuous, with member state legal systems are examined.