Vienna Convention on the Law of Treaties (1969)

The Vienna Convention on the Law of Treaties — sometimes called the "treaty of treaties" — codifies the rules governing how international treaties are made, interpreted, amended, and terminated. Adopted in 1969 and in force since 1980, it establishes foundational principles including pacta sunt servanda (agreements must be kept) and good faith performance. Relevant to the 3L framework as a key instrument defining the legal architecture within which voluntary inter-state and sub-state agreements operate, and as a model for how binding commitments between parties with different legal systems can be structured.