Pacta Sunt Servanda

Pacta sunt servanda is the principle that treaties in force bind the parties and must be performed by them in good faith. It is codified in Article 26 of the Vienna Convention on the Law of Treaties, 1969, which entered into force on 27 January 1980, and it is reinforced by Article 27, barring a party from invoking internal law to justify non-performance. In the law of the sea, the principle underlies UNCLOS Article 300, which requires states to fulfill their convention obligations in good faith and not abuse their rights. It is a foundational rule of customary international law applicable to all treaty relations.