This article analyzes new developments in the interaction between international investment law and EU law. The analysis focuses on the consequences resulting from the recent changes that have been introduced by the Lisbon Treaty and the jurisprudence of the ECJ. The author argues that the new exclusive competence of the EU regarding foreign direct investment (FDI) will have major implications for the existing Member States’ BITs as well as for the interaction with international investment law. While it is too early for a full assessment of this new situation, it has already become clear that the European institutions and the supremacy of EU law will significantly reduce the powers of the Member States, thereby fundamentally changing the current situation. Throughout this process, ensuring legal security for investors and Contracting Parties will become of utmost importance.