The Vienna Convention on the Law of Treaties (VCLT) is an international agreement regulating treaties between states. Known as the "treaty on treaties", it establishes comprehensive rules, procedures, and guidelines for how treaties are defined, drafted, amended, interpreted, and generally operated. An international treaty is a written agreement between international law subjects reflecting their consent to the creation, alteration, or termination of their rights and obligations. The VCLT is considered a codification of customary international law and state practice concerning treaties.