Introduction

With the EU assuming competence for foreign direct investment under the Lisbon Treaty, the European Commission (EC) is now also seeking a wider role in investment disputes involving EU Member States. Against this background, we revisit the existing procedural law and practice relating to the participation of non-parties in investment treaty arbitration proceedings (section III.) before assessing whether the EC's latest ambitions "to participate in the procedure" can be reconciled with the existing procedural framework (section IV.).