Pacta sunt servanda (Latin for "pacts must be respected") is a Brocard, a basic principle of civil law and of international law.

In its most common sense, it refers to private contracts, stressing that contained pacts and clauses are law between the parties, and implies that the non-fulfilment of respective obligations is a breach of the pact. The general principle of correct behaviour in commercial praxis, that also implies the bona fide, is a requirement for the efficacy of the whole system, so the eventual disorder is sometimes punished by the law of some systems even without a direct damage suffered by any of the parties.

With reference to international agreements, "every treaty in force is binding upon the parties to it and must be performed by them in good faith" (in the words of the Vienna Convention on the Law of Treaties, 1969, art. 26, and the Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations , 1986, art. 26).