Treaty-based investment arbitration has yielded a number of awards that have recognised various principles of international law that apply to investment treaty disputes. However, despite the multitude of awards, it has been observed that there has been little consistency in the application of these principles, and that achieving a ‘ jurisprudence constante’ remains a distant dream as of today. One such example is the interpretation of essential security interests clauses that exist in differentiated languages across various international investment agreements. This paper aims to analyse the various turns that jurisprudence on this aspect has taken, ranging from emphasis upon customary international law as contained in the work product of the International Law Commission, to reliance on the case law of other dispute settlement bodies such as the WTO system. In this milieu, this article demonstrates that in a pair of arbitrations against the Republic of India, the respective tribunals created coherence, despite sophisticated variations in the terms employed in the relevant treaties. What is apparent is a return to the basic rules of treaty interpretation and ascertaining the host State’s responsibility using the principles found in the Vienna Convention on the Law of Treaties, rather than relying upon circumstances precluding wrongfulness in customary international law.