Clausula rebus sic stantibus is a clause in international conventions (international agreements or treaties) that provides for the unenforceability of a treaty due to fundamentally changed circumstances. The doctrine is one of the oldest norms of customary international law. See Elihu Lauterpacht, International Law: Disputes, War and Neutrality, pts. IX-XIV, at 14-15 (Cambridge, 2004). A variant of this doctrine is codified in Article 62 of the Vienna Convention on the Law of Treaties. It is commonly codified as a provision in individual treaties.