Pacta Sunt Servanda

Pacta sunt servanda, agreements must be kept, is the principle that a binding treaty or contract obligates the parties who entered it, so that its terms function as law between them and a breach is treated as a legal wrong rather than merely a broken promise. Its earliest documented statement is usually traced to the thirteenth-century canonist Cardinal Hostiensis, though tradition also connects it to Cicero's De Legibus in the fuller form pacta sunt servanda pietate, let vows be piously performed, reflecting the principle's roots in moral and religious as much as legal obligation. In contract law, both common law and civil law systems build on the principle alongside a duty of good faith, though jurisdictions differ over how strictly and how broadly that duty is measured. In international law, pacta sunt servanda requires a state that has bound itself by treaty to perform its obligations in good faith, a requirement codified in the Vienna Convention on the Law of Treaties, which also bars a state from invoking its own domestic law as an excuse for non-performance; the principle is qualified in extraordinary circumstances by peremptory norms, jus cogens, and by the doctrine of clausula rebus sic stantibus, which allows relief where the fundamental circumstances underlying a treaty have themselves changed.