The article explores the main problematic issues of treaty interpretation: nature, concepts, and functions. It has been proved that treaty interpretation is a process carried out in international litigation, the purpose of which is to establish the true content of a treaty via defining its normative essence by giving due meaning to contradictory terms (provisions) to be used in international disputes, provided by the VCLT or developed by judicial practice. Treaty interpretation is not a political or legislative process. The rules of interpretation, defined by the VCLT, remain relevant today; however, they require interpretation that would correspond to modern realities.