In 2004, and for the first time, the question of piercing the corporate veil of a company, upon request of a State, in order to deny the protection of a Bilateral Investment Treaty appeared in front of a ICSID Tribunal. The present work offers a broad overview of the main arguments used by the different Tribunals seized of the matter as well as a comprehensive reflexion on the positions of scholars and arbitrators on the question. This work is concluded by an outline of the different solutions available.