Vienna Convention on the Law of Treaties

The Vienna Convention on the Law of Treaties (VCLT) is an international agreement regulating treaties between states.[3] Known as the "treaty on treaties", it establishes comprehensive rules, procedures, and guidelines for how treaties are defined, drafted, amended, interpreted, and generally operate.[4] The VCLT is considered a codification of customary international law and state practice concerning treaties.[5]

Vienna Convention on the Law of Treaties
Vienna Convention on the Law of Treaties
Signed23 May 1969
Effective27 January 1980
ConditionRatification by 35 states[1]
Parties116 (as of January 2018)[2]
DepositaryUN Secretary-General
LanguagesArabic, Chinese, English, French, Russian and Spanish[1]
Vienna Convention on the Law of Treaties at Wikisource

The Convention was adopted and opened to signature on 23 May 1969,[6][1] and entered into force on 27 January 1980.[1] It has been ratified by 116 states as of January 2018.[2] Some non-ratifying parties, such as the United States, recognize parts of it as a restatement of customary law and binding upon them as such.[7]

The VCLT is regarded as one of the most important instruments in treaty law, and remains an authoritative guide in disputes over treaty interpretation.[8]


The VCLT was drafted by the International Law Commission (ILC) of the United Nations, which began work on the convention in 1949.[6] During the twenty years of preparation, several draft versions of the convention and commentaries were prepared by special rapporteurs of the ILC, which included prominent international law scholars James Brierly, Hersch Lauterpacht, Gerald Fitzmaurice and Humphrey Waldock.[6]

In 1966, the ILC adopted 75 draft articles which formed the basis for the final work.[9] Over two sessions in 1968 and 1969, the Vienna Conference completed the Convention, which was adopted on 22 May 1969 and opened for signature the following day.[6][9]

Content and effects

The convention codifies several bedrocks of contemporary international law. It defines a treaty as "an international agreement concluded between states in written form and governed by international law", as well as affirming that "every state possesses the capacity to conclude treaties". Article 1 restricts the application of the Convention to written treaties between States, excluding treaties concluded between the states and international organizations or international organizations themselves. Article 26 defines pacta sunt servanda, article 53 proclaims peremptory norm and article 62 proclaims Fundamental Change of Circumstance.

The Convention has been referred to as the "treaty on treaties";[10] it is widely recognized as the authoritative guide regarding the formation and effects of treaties. Even those countries who have not ratified it recognize its significance. For example, the United States recognizes that parts of the Convention constitute customary law binding on all nations.[7] In India, the Supreme Court has also recognised the customary status of the convention.[11]


The Convention applies only to treaties which came after the convention was made and to those concluded between states, and therefore does not govern agreements between states and international organizations or between international organizations themselves; however, if any of its rules are independently binding on such organizations, they remain so.[12] The VCLT applies to treaties between states within an intergovernmental organization.[13]

However, agreements between states and international organizations, or between international organizations themselves, are governed by the 1986 Vienna Convention on the Law of Treaties between States and International Organizations or Between International Organizations if it enters into force. Furthermore, in treaties between states and international organizations, the terms of the Convention still apply between the state members.[12] The Convention does not apply to non-written agreements.[12]

Parties to the convention

As of January 2018, there are 116 state parties that have ratified the convention, and a further 15 states have signed but have not ratified the convention.[2] In addition, the Republic of China (Taiwan), which is currently only recognized by 14 UN member states, signed the Convention in 1970 prior to the UN General Assembly's vote to transfer China's seat to the People's Republic of China (PRC) in 1971; the PRC subsequently acceded to the Convention.[2] Sixty-six UN member states have neither signed nor ratified the Convention.

Vienna formula

International treaties and conventions contain rules about what entities could sign, ratify or accede to them. Some treaties are restricted to states that are members of the UN or parties to the Statute of the International Court of Justice. In rare cases there is an explicit list of the entities that the treaty is restricted to. More commonly the aim of the founding signatories is that the treaty is not restricted to particular states only and so a wording like "this treaty is open for signature to States willing to accept its provisions" is used (the so-called "All States formula"[14]).

When a treaty is open to "States", for the depositary authority[15] it is difficult or impossible to determine which entities are States. If the treaty is restricted to Members of the United Nations or Parties to the Statute of the International Court of Justice, there is no ambiguity. However, a difficulty has occurred as to possible participation in treaties when entities which appeared otherwise to be States could not be admitted to the United Nations, nor become Parties to the Statute of the International Court of Justice owing to the opposition, for political reasons, of a permanent member of the Security Council or have not applied for ICJ or UN membership. Since that difficulty did not arise as concerns membership in the specialized agencies, where there is no "veto" procedure, a number of those States became members of specialized agencies, and as such were in essence recognized as States by the international community. Accordingly, and in order to allow for as wide a participation as possible, a number of conventions then provided that they were also open for participation to States members of specialized agencies. The type of entry-into-force clause used in the Vienna Convention on the Law of Treaties was later called the "Vienna formula" and its wording was used by various treaties, conventions and organizations.[16]

Some treaties that use it include provisions that in addition to these States any other State invited by a specified authority or organization (commonly the United Nations General Assembly or an institution created by the treaty in question) can also participate, thus making the scope of potential signatories even broader.

The present Convention shall be open for signature by all States Members of the United Nations or of any of the specialized agencies or of the International Atomic Energy Agency or parties to the Statute of the International Court of Justice, and by any other State invited by the General Assembly of the United Nations to become a party to the Convention, as follows: until 30 November 1969, at the Federal Ministry for Foreign Affairs of the Republic of Austria, and subsequently, until 30 April 1970, at United Nations Headquarters, New York.

Vienna Convention on the Law of Treaties, Article 81, Signature

Interpretation of treaties

Articles 31-33 of the VCLT entail principles for interpreting conventions, treaties etc. These principles are recognized as representing customary international law, for example by the International Law Commission (ILC).[17]

The interpretational principles codified in article 31 are to be used before applying those of article 32 as the latter provision explicitly states it offers supplementary means of interpreting.

The European Court of Justice has also applied the interpretational provisions of the VCLT in different cases, including the Bosphorus Queen Case (2018)[18] where the court interpreted the extent of the term ‘any resources’ in article 220(6) of UNCLOS.[19]

See also


  1. Vienna Convention on the Law of Treaties, pg. 1
  2. "Vienna Convention on the Law of Treaties". United Nations Treaty Series. Retrieved 17 April 2016.
  3. "Vienna Convention on the Law of Treaties | History & Summary". Encyclopedia Britannica. Retrieved 26 July 2019.
  4. "Vienna Convention on the Law of Treaties (1969)". doi:10.1093/law:epil/9780199231690/law-9780199231690-e1498. Retrieved 26 July 2019.
  5. "50 Years Vienna Convention on the Law of Treaties". (in German). Retrieved 12 November 2019.
  6., Law of treaties Archived 17 October 2013 at the Wayback Machine, International Law Commission, last update: 30 June 2005. Consulted on 7 December 2008.
  7. United States Department of State. "Is the United States a party to the Vienna Convention on the Law of Treaties?". Retrieved 15 September 2015.
  8. "50 Years Vienna Convention on the Law of Treaties". (in German). Retrieved 12 November 2019.
  9. Brownlie, Ian (1998). Principles of Public International Law (5th ed.). Oxford University Press. pp. 607–08. ISBN 978-0-19-876299-7.
  10. "Vienna Convention on the Law of Treaties (1969)". Cite journal requires |journal= (help)
  11. "Guest Post: Indian Court embraces the Vienna Convention on Law of Treaties". 2 April 2015.
  12. Article 3 of the Convention.
  13. Articles 2 and 5 of the Convention
  14. All States are defined as all UN member states and states about which there are individual statements of inclusion by the UN Secretary-General or other UN organ. Repertory of Practice of United Nations Organs Supplement No. 8; page 10, UN THE WORLD TODAY (PDF); the United Nations Secretary-General has stated that when the "any State" or "all States" formula is adopted, he would be able to implement it only if the General Assembly provided him with the complete list of the States coming within the formula, other than those falling within the "Vienna formula"UN Office of Legal Affairs
  15. The UN Secretary-General or some other competent authority defined in the treaty in question, e.g. Switzerland for the Geneva Conventions – see special cases.
  16. UN Legal Affairs the so-called "Vienna formula".
  17. ILC, Fragmentation of international law: difficulties arising from the diversification and expansion of international law, Report A/CN.4/L.682 (presented at the 58th session in Geneva, 1 May – 9 June and 3 July – 11 August 2006) 89, para 168
  18. Case C-15/17 Bosphorus Queen Shipping Ltd Corp vs Rajavartiolaitos, ECLI:EU:C:2018:557, para 67.
  19. Interpreting the "discharge-term" of article 218 (1) of UNCLOS in accordance with article 31 of the VCLT to allow the term to encompass emissions has also been discussed. See Jesper Jarl Fanø (2019) Enforcing International Maritime Legislation on Air Pollution through UNCLOS. Hart Publishing.
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