The EU’s participation in international dispute resolution mechanisms presents particular problems owing to its multilevel governance and its autonomy from international and national law. The inclusion of foreign direct investment in the Common Commercial policy in the Treaty of Lisbon, expanded those to investment arbitrations under Member States’ BITs, as the Court of Justice ruled in Achmea. EU Law and International Investment Arbitration, examines the impact of that inclusion beyond Achmea, from the perspectives of international and EU law, to the remaining extra-EU BITs of the Member States and the Energy Charter Treaty.