The International Court of Justice and the Court of Justice of the European Union: Between Fragmentation and Universality of International Law

Abstract

This chapter discusses how the Court of Justice of the European Union (CJEU) has used judgments of the International Court of Justice (ICJ) in its legal reasoning. The CJEU uses ICJ jurisprudence in three main ways: when discussing customary international law, when applying the law of treaties, and when using international law to interpret and develop principles of EU law. The chapter reviews the cases in which the CJEU and the Advocates General have discussed ICJ cases, including areas of international humanitarian law, diplomatic and consular law, nationality and citizenship, the law of the sea, and the international law of treaties. On the one hand, the CJEU’s use of ICJ case law may show its commitment to the universality and coherence of international law. However, the CJEU also has a strong commitment to the coherence and unity of EU law, and has emphasised the autonomy of the EU legal order. The chapter shows that, upon closer inspection, the CJEU interprets and applies ICJ jurisprudence through an EU law prism. It also shows that, over time, principles of international law are transformed into principles of EU law. In these instances, the CJEU no longer refers to ICJ/PCIJ jurisprudence, but as autonomous EU law principles. ICJ jurisprudence is used to fill gaps, or to support certain legal arguments, but it is not followed as if it were a hierarchically superior court.