The case study of investment treaty arbitration provides an opportunity to examine whether and how the invocation of responsibility by a non-State actor has affected secondary rules of State responsibility. This article takes the analytical perspective of investors, capable of being perceived as right-holders (by reference to human and consular rights), beneficiaries (by reference to the law of treaties rules on third States), or agents (by reference to diplomatic protection). The shift from the State to the investor as the entity invoking responsibility for the breach of investment treaties seems to have influenced the law of State responsibility in a number of distinct ways. The apparent disagreement about the law of State responsibility may sometimes really relate to questions of treaty interpretation, while in other cases rules from an inter-State context are applied verbatim. At the same time, the different perspectives lead to importantly different conclusions regarding circumstances precluding wrongfulness, elements of remedies, waiver of rights and, possibly, interpretative relevance of diplomatic protection rules. The overall thesis is that conceptual challenges faced by investment arbitration may be illuminated by the solutions provided by the regimes that provided the background for its creation.

*Please note: This paper was published in the European Journal of International Law, Volume 24, issue 2. It can be found on the EJIL website.