The impact of European Union law on investment arbitration proceedings arising from intra-EU and extra-EU bilateral investment agreements (BITs) remains matter of considerable debate. In the last years several arbitral tribunals expressed their view on the subject matter, raising constant suspicion by the European Commission and certain EU-member states involved in such proceedings. The book hence analysis the potential objections regarding the arbitral tribunal's jurisdiction and the merits of the case resulting from the interference of European Union law with international investment law. Although such consequence is disputed by several arbitral tribunals, the author supports that in intra-EU proceedings the tribunals lack jurisdiction. However, in extra-EU proceedings, the author suggests to transpose the Bosphorus judgement rendered by the European Court of Human Rights to investment arbitration proceedings to reduce potential conflicts and satisfy the diverging interests.