Abstract: This article aims at presenting the difficulties encountered in the enforcement of the arbitration award by which a foreign investor has obtained compensation against the host State, member of the European Union as a result of non-compliance with a Bilateral Investment Treaty. The damages considered by the European Commission to be incompatible with the rules of the union and the obligation on the state to recover the sums paid, have brought to the forefront the relationship between international law and EU law, a relationship on which the European courts are now called upon.

Keywords: investor; intra-UE BIT; arbitration award; compensation; new aid.