Which of the following customary principles of International law has been codified and mentioned in…

Article 26 of the Vienna Convention on the Law of Treaties, 1969, headed "Pacta Sunt Servanda", codifies the customary rule that every treaty in force is binding upon the parties to it and must be performed by them in good faith. The "Theory of consent", the "Auto limitation theory" and the "Theory of Fundamental Rights" are theories explaining the basis of international obligation, not rules codified in Article 26.