Marking the 50th anniversary of the influential ERTA doctrine, this book analyses and contextualises the entire breadth of the jurisprudence of EU external relations law through a systematic, case-by-case account of the field. The entire framework of EU external relations law has been built from the ground up by the jurisprudence of the Court of Justice of the European Union. At the beginning of the field’s emergence, the legal questions to be answered concerned the division of powers and competence between, firstly, the Member States and that of the Union; and secondly, the division of powers and competence between the different institutions of the Union. Questions on such matters continue to be asked, but more contemporarily, new legal questions have arisen that have been in need of adjudication, including questions concerning the autonomy of Union law; the relationship between the Union and other international organisations; the relationship between Union law and international law; the scope and breadth of international agreements; amongst others. The book features established academic scholars, judges, agents of institutions and Member States, and legal practitioners in the field of EU external relations law, analysing over 90 cases in which the Court has legally shaped the theory and practice of the external dimension of legal Europe. Cited in Opinion of Advocate General Nicholas Emiliou in Case C-516/22, European Commission v United Kingdom of Great Britain and Northern Ireland, ECLI:EU:C:2023:857 (Judgment of the UK Supreme Court), Court of Justice of the European Union, 9 November 2023; and, Opinion of Advocate General Nicholas Emiliou in Case C 728/23 P, Kingdom of Spain v Robert Stockdale, Council of the European Union, European Commission, European External Action Service (EEAS), European Union Special Representative in Bosnia and Herzegovina, ECLI:EU:C:2025:710, Court of Justice of the European Union, 18 September 2025.
