Foreign investment protection is a controversial topic within the EU. Due to public opposition and the need for EU investment agreements to be ratified by all Member States, it will most likely take decades to replace the existing BITs between Member States and third countries, with EU-wide agreements. The transitional mechanism regulating these extra-EU BITs, which allows the Commission a measure of control over Member States’ investment policies, is becoming ever more important. There is a significant gap between what is said with regard to investment reform (for example, the aim to create a Multilateral Investment Court) and what is actually done (over a hundred BITs were signed or ratified in the past decade—every single one referring disputes to classic arbitration). After having been in force for a decade, the time is ripe for an in-depth assessment of the successes and failures of this mechanism, giving an insight into this aspect of the EU legal order and its constitutionalisation process.