The Vienna Convention on the Law of Treaties (VCLT) is an international agreement that regulates treaties among sovereign states.
Known as the "treaty on treaties", the VCLT establishes comprehensive, operational guidelines, rules, and procedures for how treaties are drafted, defined, amended, and interpreted. The VCLT defines a treaty as an international agreement in writing concluded between states governed by international law.
A treaty is a recorded international agreement between sovereign states or other subjects of international law (including international organizations) that is governed by international law. A treaty may also be known as an international agreement, protocol, covenant, convention, pact, or exchange of letters, among other terms; however, only documents that are legally binding on the parties are considered treaties under international law. Treaties may be bilateral (between two countries) or multilateral (involving more than two countries).
International agreements were used in some form by most major civilizations and became increasingly common and more sophisticated during the early modern era. The early 19th century saw developments in diplomacy, foreign policy, and international law reflected by the widespread use of treaties. The 1969 Vienna Convention on the Law of Treaties (VCLT) codified these practices and established rules and guidelines for creating, amending, interpreting, and terminating treaties, and for resolving disputes and alleged breaches.
In international law, a depositary is a government or organization to which a multilateral treaty is entrusted. The principal functions of a depositary are codified in Article 77 of the Vienna Convention on the Law of Treaties.
Customary international law consists of international legal obligations arising from established or usual international practices, which are less formal customary expectations of behavior often unwritten as opposed to formal written treaties or conventions. Customary law is also referred to as opinio juris (means “opinion of law”), which is a term used in international law to signifiy state practices taken under the belief that such actions are legal obligations. Generally, customary international law applies equally to all states. Along with general principles of law and treaties, custom is considered by the International Court of Justice, jurists, the United Nations, and its member states to be among the primary sources of international law.
Rules that are considered customary law are binding upon all states. Customary international law need not be codified in a treaty. If a treaty, or any portion thereof, becomes customary law, it will bind all states that are not persistent objectors. A treaty or international agreement can bind a state not party to the treaty when: the treaty codifies customary international law; or when the treaty has become customary law or represents an obligation erga omnes. For example, the Vienna Convention on the Law of Treaties is widely described as codifying customary international law concerning treaties.
A reservation in international law is a caveat to a state's acceptance of a treaty. A reservation is defined by the 1969 Vienna Convention on the Law of Treaties (VCLT) as:
In effect, a reservation allows the state to be a party to the treaty, while excluding the legal effect of that specific provision in the treaty to which it objects.States cannot take reservations after they have accepted the treaty; a reservation must be made at the time that the treaty affects the State. The Vienna Convention did not create the concept of reservations but codified existing customary law. Thus even States that have not formally acceded to the Vienna Convention act as if they had. As reservations are defined under the Vienna Convention and interpretative declarations are not, the two are sometimes difficult to discern from each other. Unlike a reservation, a declaration is not meant to affect the State's legal obligations but is attached to State's consent to a treaty to explain or interpret what the State deems unclear.
The Geneva Conventions, which were most recently revised in 1949, consist of seven individual treaties which are open to ratification or accession by any sovereign state. They are:
The four 1949 Conventions have been ratified by 196 states, including all UN member states, both UN observers (the Holy See and the State of Palestine), as well as the Cook Islands. The Protocols have been ratified by 175, 170 and 80 states respectively. In addition, Article 90 of Protocol I states that "The High Contracting Parties may at the time of signing, ratifying or acceding to the Protocol, or at any other subsequent time, declare that they recognize ipso facto and without special agreement, in relation to any other High Contracting Party accepting the same obligation, the competence of the [International Fact-Finding] Commission to enquire into allegations by such other Party, as authorized by this Article." 77 states have made such a declaration.