Vienna Convention on the Law of Treaties (1969): VCLT Guide
- Edmarverson A. Santos
- Nov 11, 2024
- 36 min read
Updated: 5 days ago
Introduction
The Vienna Convention on the Law of Treaties is the principal multilateral convention governing the law of treaties between States. Adopted in 1969 and in force since 1980, the VCLT provides rules on treaty formation, consent, reservations, observance, interpretation, amendment, invalidity, termination, withdrawal, and suspension. It supplies much of the legal framework through which States create and manage binding treaty obligations (United Nations, 1969).
Treaties regulate subjects as different as international boundaries, diplomatic relations, trade, human rights, environmental protection, maritime rights, arms control, and international organizations. Those regimes differ substantially in content, but disputes concerning them often raise the same preliminary questions. Lawyers may need to determine whether an instrument is legally a treaty, whether a representative could bind the State, when consent became effective, how a disputed clause should be interpreted, or whether withdrawal is legally available.
The Convention is also important beyond the obligations owed by its own parties. International courts and tribunals have recognized that a number of VCLT provisions reflect customary international law. The International Court of Justice has consequently applied rules expressed in the Convention to treaties concluded before the VCLT entered into force and in circumstances where the relevant rule operated independently as custom (ICJ, 1997; ICJ, 1999).
That wider influence should not be overstated. The 1969 Convention directly governs treaties within its material and temporal scope; it does not make every international agreement a treaty, and it does not convert every one of its 85 articles into customary law. Questions involving treaties with international organizations, State succession, State responsibility, or the effects of armed conflict may require other legal sources. Understanding the VCLT requires attention to both its authority and its limits.
1. Vienna Convention on the Law of Treaties at a Glance
The Vienna Convention on the Law of Treaties was adopted by the United Nations Conference on the Law of Treaties on 22 May 1969 and opened for signature on 23 May 1969. Article 84 provided for its entry into force after the thirty-fifth instrument of ratification or accession had been deposited. That condition was satisfied, and the Convention entered into force on 27 January 1980 (United Nations, 1969).
The Secretary-General of the United Nations is the depositary. As of 26 August 2026, the United Nations Treaty Collection records 119 parties to the Convention. Formal participation should be distinguished from the separate question whether a particular VCLT rule also binds other States as customary international law (United Nations Treaty Collection, 2026a).
The Convention contains a preamble, 85 articles, and an annex. Its structure follows much of the legal life of a treaty: scope and definitions, conclusion and entry into force, observance, application, interpretation, amendment, modification, invalidity, termination, suspension, procedural consequences, depositary functions, registration, and final provisions.
Certain provisions recur particularly often in legal practice and academic analysis:
VCLT provision | Main subject |
Articles 1–3 | Scope, definition of a treaty, and agreements outside the Convention |
Article 4 | Non-retroactivity of the Convention |
Articles 6–8 | Capacity, full powers, and unauthorized acts |
Articles 11–17 | Means of expressing consent to be bound |
Article 18 | Obligation not to defeat a treaty's object and purpose |
Articles 19–23 | Reservations, acceptance, objections, and procedure |
Article 25 | Provisional application |
Article 26 | Pacta sunt servanda |
Article 27 | Internal law and treaty performance |
Articles 28–30 | Time, territory, and successive treaties |
Articles 31–33 | Treaty interpretation |
Articles 34–38 | Treaties and third States |
Articles 39–41 | Amendment and modification |
Articles 42–45 | General rules on validity, continuance, separability, and loss of rights |
Articles 46–52 | Grounds affecting consent or treaty validity |
Article 53 | Conflict with existing jus cogens |
Articles 54–64 | Termination, withdrawal, and suspension |
Article 64 | Emergence of a new jus cogens norm |
Articles 65–68 | Procedure concerning invalidity and termination |
Articles 69–72 | Consequences of invalidity, termination, and suspension |
Articles 76–80 | Depositaries, notifications, corrections, and registration |
The table is a guide to the Convention rather than a substitute for its text. Several legal problems require provisions to be read together. A withdrawal dispute may involve the treaty's own clauses, Articles 54 or 56, procedural requirements under Article 65, and the consequences specified in Article 70. Interpretation likewise cannot be reduced to Article 31(1) without considering the rest of Articles 31–33 where relevant.
2. Codification, Adoption, and Legal Authority
The VCLT did not create the law of treaties from the beginning. States had concluded treaties for centuries, and international law already contained rules concerning consent, interpretation, performance, invalidity, and termination. The postwar codification project sought to organize and clarify much of that law while addressing areas in which State practice or legal doctrine remained unsettled.
Codification was not simply transcription. Some provisions largely restated existing customary rules, whereas others developed the law or embodied compromises reached during the International Law Commission and diplomatic conference processes. Reservations are a prominent example. The VCLT incorporated the object-and-purpose approach associated with the ICJ's 1951 advisory opinion on reservations to the Genocide Convention while providing a more detailed framework for acceptance, objection, and legal consequences (ICJ, 1951; United Nations, 1969).
The distinction between codification and progressive development remains legally significant. A State is bound by the VCLT as a treaty only when the Convention applies to it under ordinary rules of treaty law. If a VCLT provision is invoked outside that relationship, its applicability must rest on another legal basis, most commonly a corresponding rule of customary international law.
The Convention's authority is consequently neither confined to its formal parties nor identical for every provision. A careful legal argument should specify whether it relies on the VCLT as treaty law, on a customary rule reflected in the VCLT, or on the Convention as persuasive evidence of the structure of treaty law.
2.1 The International Law Commission
The International Law Commission placed the law of treaties on its program of work at its first session in 1949. James Brierly, Hersch Lauterpacht, Gerald Fitzmaurice, and Humphrey Waldock successively served as Special Rapporteurs. The project evolved substantially during that period, including a shift from a possible model code toward draft articles capable of becoming a multilateral convention (Zemanek, 2009).
Waldock's reports during the 1960s supplied much of the structure eventually presented to States. In 1966, the Commission adopted its final Draft Articles on the Law of Treaties with commentaries and recommended the convening of an international conference of plenipotentiaries (International Law Commission, 1966).
The commentaries remain useful for understanding why particular formulations were selected and how the Commission understood the relationship between the draft provisions. They also record legal authorities and State practice considered during codification. Their value is interpretive and historical; they are not part of the Convention and are not independently binding rules.
This distinction becomes especially important where the final treaty text differs from an earlier draft or where a commentary discusses an issue that the Convention itself leaves unresolved. The commentary may illuminate the drafting history without displacing the authentic treaty text adopted by States.
2.2 Adoption, entry into force, and customary law
The United Nations Conference on the Law of Treaties met in Vienna in 1968 and 1969. States debated the ILC draft, proposed amendments, and negotiated matters that carried significant legal and political consequences. The Convention was adopted on 22 May 1969 and opened for signature the following day (United Nations, 1969).
It entered into force on 27 January 1980. The passage of more than a decade between adoption and entry into force illustrates an elementary point of treaty law: adoption of a text, signature, consent to be bound, and entry into force are distinct legal events.
The Convention's formal entry into force did not mean that treaty law suddenly began in 1980. In Gabčíkovo-Nagymaros Project, the ICJ observed that some rules contained in the Convention could be regarded as codifications of existing customary law. In Kasikili/Sedudu Island, the Court used rules of treaty interpretation reflected in the VCLT when interpreting an Anglo-German agreement concluded in 1890 (ICJ, 1997; ICJ, 1999).
Those decisions do not support a claim that every VCLT provision is customary. The customary character of a rule must be established with respect to the particular proposition being invoked. Treaty participation and customary obligation remain distinct legal bases even when their substantive content coincides.
3. What Counts as a Treaty
Treaty law begins with classification. International relations produce conventions, agreements, protocols, exchanges of notes, joint declarations, memoranda, agreed minutes, communiqués, and many other instruments. The title selected by governments does not itself determine whether the instrument creates obligations governed by international law.
Article 2(1)(a) defines a treaty for purposes of the VCLT as an international agreement concluded between States in written form and governed by international law, whether embodied in one instrument or in two or more related instruments and regardless of its designation (United Nations, 1969, art. 2(1)(a)).
The decisive question is legal character rather than terminology. Instruments carrying formal titles may be non-binding, while documents with informal titles may constitute treaties. Classification affects the availability of treaty-law rules concerning interpretation, reservations, amendment, invalidity, termination, and other matters.
Political importance is also separate from legal status. A joint political declaration may influence international relations considerably without creating treaty obligations. Conversely, a technically narrow exchange of notes may constitute a binding international agreement even if it attracts little public attention.
3.1 Written agreements between States
The VCLT definition contains several elements. The agreement must be between States, be in written form, and be governed by international law. A commercial contract entered into by a government under a national legal system does not become a treaty simply because a State is one of the contracting parties.
An international agreement does not need to appear in a single document. Article 2 expressly contemplates agreements contained in two or more related instruments. Article 13 further recognizes exchange of instruments as a means of expressing consent when the instruments provide that their exchange will have that effect or when that intention is otherwise established (United Nations, 1969, art. 13).
Exchange of notes has long been used for practical bilateral arrangements. One State may send a note setting out agreed terms and the other reply that those terms are accepted. Where the instruments objectively manifest an agreement governed by international law, the pair of documents may together constitute a treaty.
The VCLT's written-form requirement concerns its own scope. Article 3 expressly prevents an inference that non-written agreements or agreements involving other subjects of international law are necessarily without legal effect. Their validity and governing rules must be assessed under the international law applicable to those instruments.
3.2 Legal effect does not depend on the label
The legal inquiry is objective. The text of the instrument and the circumstances of its conclusion must be examined to determine whether the parties manifested an intention to create rights and obligations governed by international law. A private, unexpressed intention of one negotiator cannot by itself convert a political arrangement into a treaty or deprive an otherwise binding agreement of legal effect.
The ICJ's 1994 judgment in Maritime Delimitation and Territorial Questions between Qatar and Bahrain illustrates the point. The Court examined exchanges of letters and signed minutes and concluded that they constituted international agreements creating rights and obligations for the parties. The documents' comparatively informal form did not prevent them from having treaty status (ICJ, 1994).
The decision should not be read as establishing that diplomatic minutes are normally treaties. Their status depends on the particular text and circumstances. Wording that records agreed commitments, specifies obligations, or establishes procedures may support a finding of legal intent, but no single formula is universally decisive.
Article 3 reinforces the distinction between the scope of the VCLT and the existence of international legal obligations. An agreement outside the Convention's definition may still be legally valid, while rules expressed in the VCLT may sometimes apply to it independently through other rules of international law (United Nations, 1969, art. 3).
4. Capacity, Representation, and Consent
A treaty becomes binding through acts attributable to States, but governments necessarily act through human representatives. Treaty law must therefore distinguish the State's capacity to conclude treaties from the authority of a particular person and from the legal act by which consent to be bound is expressed.
The distinction has practical consequences. A representative may have authority to negotiate or adopt a treaty text without authority to express the State's final consent. Signature may itself bind the State in one treaty while merely authenticating the text and preceding ratification in another.
Domestic constitutional procedures form a further layer. Parliamentary approval, executive authorization, or judicial review may determine what a government can do internally, but those domestic steps should not automatically be equated with the international acts through which consent is expressed.
4.1 Capacity and full powers
Article 6 states that every State possesses capacity to conclude treaties. Treaty-making capacity follows from statehood, although domestic constitutional law ordinarily determines which organs may exercise that capacity and through what procedures (United Nations, 1969, art. 6).
Article 7 regulates representation. A person may represent a State for purposes of concluding a treaty when appropriate full powers are produced or when the practice of the States concerned or other circumstances show that they intended to regard that person as representing the State without requiring full powers.
Certain officeholders receive authority directly from Article 7 by virtue of their functions. Heads of State, heads of government, and ministers for foreign affairs may perform all acts relating to treaty conclusion without producing full powers. Heads of diplomatic missions have more limited authority for adopting treaty texts between the accrediting and receiving States, while accredited representatives to international conferences or organizations may adopt treaty texts within the relevant forum.
An act performed without the authority required by Article 7 is not necessarily beyond repair. Article 8 provides that an unauthorized act relating to treaty conclusion has no legal effect unless subsequently confirmed by the State. Confirmation converts what was initially unauthorized into an act attributable to the State for treaty purposes (United Nations, 1969, art. 8).
4.2 Signature, ratification, accession, and exchange
Article 11 recognizes several methods for expressing consent to be bound: signature, exchange of instruments constituting a treaty, ratification, acceptance, approval, accession, or another agreed means. Which method applies depends on the treaty and the circumstances of its conclusion (United Nations, 1969, art. 11).
Signature has no single legal effect. Under Article 12, it expresses consent when the treaty provides that signature will have that effect, when the negotiating States so agreed, or when that intention appears from the representative's full powers or was expressed during negotiations. Where the treaty is subject to ratification, signature ordinarily precedes a later act of consent.
Ratification allows a State to confirm internationally that it accepts the treaty after signature, often following domestic constitutional procedures. Acceptance and approval may perform legally comparable functions. Accession allows a State to express consent without using the prior signature-and-ratification sequence where the treaty or the parties permit accession.
Domestic approval should be kept analytically separate from international consent. A legislature may authorize ratification, but the domestic vote is not ordinarily the international instrument of ratification. Likewise, an executive may deposit an instrument internationally only after satisfying internal constitutional requirements. Treaty law and domestic constitutional law interact, but they regulate different legal questions.
5. Legal Effects Before Entry into Force
A State usually becomes subject to the treaty's full substantive obligations only when the treaty has entered into force for that State. The interval between signature and entry into force can nevertheless produce legal consequences. Articles 18 and 25 address two important examples.
Article 18 establishes a limited obligation concerning the treaty's object and purpose. Article 25 concerns provisional application, which may give specified treaty provisions legal effect before formal entry into force. The two rules have different bases and consequences.
Neither should be described as making signature equivalent to ratification. A State may have duties during the pre-entry period without yet being bound by the treaty in full.
5.1 Article 18 and the object and purpose obligation
Article 18 addresses two situations. A State that has signed a treaty or exchanged instruments subject to ratification, acceptance, or approval must refrain from acts that would defeat the treaty's object and purpose until it has made its intention not to become a party clear. A State that has already expressed consent to be bound is subject to the same restraint pending entry into force, provided entry into force is not unduly delayed (United Nations, 1969, art. 18).
The obligation is narrower than full treaty performance. Article 18 does not require a signatory to comply immediately with every substantive provision as if the treaty were already in force. Its concern is conduct serious enough to defeat the object and purpose of the instrument.
Determining that object and purpose is not mechanical. The treaty's text, preamble, structure, subject matter, and substantive design may all inform the inquiry. Broad policy aspirations should not be used to transform Article 18 into an obligation to implement the entire treaty prematurely.
The Article also preserves State choice. In the signature-before-ratification situation, the specific Article 18 obligation ceases once the State makes clear that it does not intend to become a party. The provision protects the treaty process without eliminating the legal distinction between signature and final consent.
5.2 Provisional application under Article 25
Provisional application rests on agreement. Article 25 permits a treaty or part of a treaty to be applied provisionally before its entry into force when the treaty itself so provides or when the negotiating States have otherwise agreed (United Nations, 1969, art. 25).
The legal effect is stronger than the restraint imposed by Article 18. The International Law Commission's 2021 Guide to Provisional Application of Treaties states that provisional application produces a legally binding obligation to apply the treaty, or the relevant part of it, according to the terms agreed for provisional application (International Law Commission, 2021).
That does not make provisional application identical to entry into force. Its legal basis, scope, duration, and termination derive from the treaty or other agreement providing for it. States may provisionally apply only certain provisions, and the provisional arrangement may contain conditions different from those governing ordinary treaty operation.
Unless the treaty or negotiating States have agreed otherwise, Article 25 provides that provisional application for a State ends when it notifies the other relevant States that it does not intend to become a party. Particular treaty regimes may establish different procedures, so Article 25 must be read with the instrument that creates the provisional arrangement.
6. Reservations to Multilateral Treaties
Reservations permit a State, when signing, ratifying, accepting, approving, or acceding to a treaty, to seek to exclude or modify the legal effect of specified treaty provisions in their application to that State. Article 2(1)(d) defines a reservation by its intended legal effect rather than by the title attached to the statement (United Nations, 1969, art. 2(1)(d)).
The mechanism facilitates participation in multilateral treaties where States agree on the larger instrument but not on every provision. That flexibility can broaden membership, but it can also produce a network of differentiated treaty relations among parties.
Articles 19–23 govern formulation, acceptance, objection, legal effects, withdrawal, and procedure. The framework is general. Particular treaties may establish stricter reservation rules or prohibit reservations entirely.
6.1 The object and purpose test
Article 19 prohibits a reservation where the treaty itself prohibits reservations, where it permits only specified reservations that do not include the proposed reservation, or where the reservation is incompatible with the treaty's object and purpose (United Nations, 1969, art. 19).
The third rule reflects the approach taken by the International Court of Justice in its 1951 advisory opinion on Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide. The Court declined to apply a universal requirement of unanimous acceptance and treated compatibility with the Convention's object and purpose as central to the reservations regime appropriate to that treaty (ICJ, 1951).
The advisory opinion preceded the VCLT and dealt specifically with the Genocide Convention. It did not determine every legal question later addressed in Articles 19–23, but its reasoning strongly influenced the codification of the general reservations regime.
The ILC's 2011 Guide to Practice on Reservations to Treaties elaborates the object-and-purpose inquiry. It describes a reservation as incompatible when it affects an essential element of the treaty necessary to its general tenor in a manner that impairs the treaty's raison d'être (International Law Commission, 2011a). The Guide is non-binding and should be used as interpretive and analytical guidance rather than as a treaty amendment.
6.2 Acceptance, objection, and legal effects
Article 20 does not impose a single acceptance regime on every treaty. A treaty may expressly require acceptance of reservations. For a treaty negotiated between a limited number of States, acceptance by all parties may be necessary where application of the treaty in its entirety among all parties was an essential condition of consent.
A reservation to the constituent instrument of an international organization normally requires acceptance by the organization's competent organ unless the treaty provides otherwise. Other multilateral treaties are governed by the more general rules in Article 20 (United Nations, 1969, art. 20).
Acceptance of a reservation by another contracting State normally establishes treaty relations between that State and the reserving State. An objection does not automatically prevent the treaty from entering into force between the objecting and reserving States. That result follows only when the objecting State definitely expresses the intention that the treaty should not enter into force between them.
Article 21 then determines the treaty consequences. Between the reserving State and an accepting State, the relevant provisions are modified to the extent of the reservation. Where a State objects but does not oppose treaty relations, the provisions affected by the reservation do not apply between those States to the extent of the reservation.
The resulting structure is relational. A multilateral treaty may have one text while operating differently between different pairs of parties. Legal analysis of a reservation should therefore identify the reservation, its permissibility, the reactions of other parties, and the resulting bilateral effects.
6.3 Reservations in human rights treaties
Human rights treaties have generated particular controversy because many of their substantive obligations are directed toward the protection of individuals rather than reciprocal exchanges of equivalent benefits between States. A reservation may affect the integrity of a supervisory regime even where other States have limited practical incentives to object.
In General Comment No. 24, the Human Rights Committee asserted that it could assess reservations to the International Covenant on Civil and Political Rights against the Covenant's object and purpose. It also took the position that an unacceptable reservation would generally be severable, leaving the State bound by the Covenant without the benefit of that reservation (Human Rights Committee, 1994, paras 17–18).
General Comment No. 24 is an influential interpretation by the treaty body charged with functions under the ICCPR, but it is not a judgment and does not itself establish a universally binding rule of treaty law. States challenged aspects of the Committee's approach, including its competence to determine the consequences of impermissible reservations and its position on severability.
The ILC later addressed the legal consequences of impermissible reservations in its 2011 Guide to Practice. Its approach is more elaborate than a simple rule that every impermissible reservation is automatically severed. The legal position may depend on the reserving State's intention concerning whether it would remain bound without the benefit of the reservation (International Law Commission, 2011a).
The broader lesson is one of legal classification. Articles 19–23 remain the general VCLT framework, while treaty-specific provisions, institutional competence, judicial decisions, treaty-body interpretations, and the reactions of States may add further layers. A system-specific approach should not be presented as the universal law governing every human rights treaty.
7. Pacta Sunt Servanda and Good Faith
Article 26 provides that every treaty in force is binding upon the parties and must be performed by them in good faith. The Latin expression pacta sunt servanda captures the binding force of treaty obligations; the same article expressly connects that force with good-faith performance (United Nations, 1969, art. 26).
The rule gives legal effect to consent after a treaty has entered into force. A State cannot ordinarily treat an international obligation as optional because implementation has become politically inconvenient, financially burdensome, or unpopular domestically.
Treaty law nevertheless provides lawful mechanisms for change. Parties may amend a treaty, agree to terminate it, invoke an applicable withdrawal clause, suspend obligations where legally permitted, or rely on one of the limited grounds in Part V. Binding force and legal change are therefore compatible rather than contradictory.
Article 26 should also be distinguished from the law of responsibility. A State that fails to perform a valid treaty may commit an internationally wrongful act, but the existence and consequences of that breach are not exhausted by the VCLT. Treaty validity, treaty operation, and responsibility remain separate legal questions.
7.1 Binding force and domestic law
Article 27 states that a party may not invoke the provisions of its internal law as justification for failure to perform a treaty. The rule protects the international legal relationship from being displaced by unilateral changes or defects in domestic law (United Nations, 1969, art. 27).
Domestic law remains highly relevant inside the State. Constitutional rules may determine whether legislative approval is required, whether treaty provisions have direct effect, how implementing legislation is enacted, and which courts may apply international obligations. Those questions do not remove the State's international obligation once valid consent has been expressed and the treaty is in force.
Article 46 concerns a narrower question at the stage of consent. A State may invoke a violation of its internal law concerning competence to conclude treaties only when the violation was manifest and concerned a rule of fundamental importance. The threshold is deliberately demanding (United Nations, 1969, art. 46).
Articles 27 and 46 should not be collapsed into a general proposition that domestic law is irrelevant to treaty relations. Internal law may be central to determining the authority and procedures through which a State acts. The VCLT restricts the circumstances in which a State can use that internal law to defeat its international consent or excuse non-performance.
7.2 Good faith in treaty performance
Good faith is a general principle with a concrete role in treaty law. In the Nuclear Tests cases, the ICJ described good faith as one of the basic principles governing the creation and performance of legal obligations. The Court's reasoning concerned unilateral declarations, but its statement reflects a broader principle also expressed directly in Article 26 of the VCLT (ICJ, 1974).
In treaty performance, good faith requires parties to carry out the obligations they have actually undertaken rather than manipulate formal compliance to frustrate those obligations. The inquiry remains tied to the treaty's terms, context, and applicable legal rules.
Good faith also appears in Article 31, which requires treaty interpretation in good faith. That recurrence does not create an unlimited power to revise agreed obligations in the name of fairness. An interpreter cannot invoke good faith to ignore clear conditions governing reservations, jurisdiction, withdrawal, or amendment.
The principle is strongest when used with legal discipline. It informs the performance and interpretation of existing obligations; it should not become a substitute source from which entirely new treaty commitments are inferred.
8. Application in Time, Territory, and Treaty Conflict
A treaty may be valid and in force while still raising questions about its temporal reach, territorial application, or relationship with other agreements. Articles 28–30 provide general rules for those problems.
These provisions are important because treaty obligations frequently overlap. A State may be party to an older bilateral agreement and a later multilateral treaty addressing related conduct, or two specialized regimes may apply simultaneously to the same factual situation.
The treaty texts themselves remain decisive. Articles 28–30 often function as default rules and must be read together with any clauses establishing territorial limits, priority rules, transitional arrangements, or special relationships with other treaties.
8.1 Non-retroactivity and territorial application
Article 28 establishes a presumption against retroactive treaty application. Unless a different intention appears from the treaty or is otherwise established, its provisions do not bind a party in relation to acts, facts, or situations that took place or ceased to exist before the treaty entered into force for that party (United Nations, 1969, art. 28).
Continuing situations require closer analysis. A historical event may have occurred before entry into force while a legally relevant situation or course of conduct continues afterward. The temporal question then depends on the treaty obligation and the nature of the facts being assessed.
Article 29 supplies the default rule on territorial scope. Unless a different intention appears from the treaty or is otherwise established, a treaty is binding upon each party in respect of its entire territory (United Nations, 1969, art. 29).
Treaties may provide otherwise. Territorial clauses, declarations, federal arrangements, colonial-era extensions, or special application provisions can alter the default position. The text and legal history of the particular treaty must therefore be checked before Article 29 is treated as conclusive.
8.2 Successive treaties and Article 103 of the UN Charter
Article 30 addresses successive treaties relating to the same subject matter. It begins by making its rules subject to Article 103 of the Charter of the United Nations. Article 103 provides that, where obligations of UN Members under the Charter conflict with obligations under another international agreement, Charter obligations prevail (United Nations, 1945, art. 103; United Nations, 1969, art. 30).
When all parties to an earlier treaty are also parties to a later treaty and the earlier treaty remains in force, Article 30 provides that the earlier treaty applies only to the extent that its provisions are compatible with the later treaty. This is more precise than a general assertion that later treaties always replace earlier ones.
The position changes when participation in the treaties differs. Between States party to both instruments, the relationship may be governed by the rules applicable to successive treaties. Between a State party to both and a State party to only one, their mutual rights and obligations are governed by the treaty to which both are parties.
Treaties may also contain their own conflict or compatibility clauses. Those provisions must be interpreted before a lawyer assumes that Article 30 alone resolves the relationship. Complex treaty regimes can require attention to membership, subject matter, priority clauses, and rules outside the VCLT.
9. Treaty Interpretation Under Articles 31–33
Articles 31–33 are among the most frequently invoked provisions of the Vienna Convention on the Law of Treaties. They establish a general method for identifying the legal meaning of treaty provisions and are regularly applied by international courts, tribunals, governments, and legal advisers.
Article 31 contains the general rule of interpretation. Article 32 provides for supplementary means in defined circumstances. Article 33 addresses treaties authenticated in two or more languages.
The International Court of Justice has repeatedly treated the interpretive rules expressed in Articles 31 and 32 as reflecting customary international law. Their importance consequently extends to treaty relationships outside the VCLT's direct temporal or personal application (ICJ, 1999).
9.1 Ordinary meaning, context, and object and purpose
Article 31(1) requires a treaty to be interpreted in good faith according to the ordinary meaning given to its terms in their context and in light of the treaty's object and purpose (United Nations, 1969, art. 31(1)).
The International Law Commission's 1966 commentary makes clear that these elements form a single combined operation rather than a set of rigidly separated tests. Ordinary meaning is assessed within context and against the treaty's object and purpose rather than exhausted in isolation before the interpreter turns to other considerations (International Law Commission, 1966).
Context includes the text, preamble, and annexes. Article 31(2) also brings within the interpretive context certain agreements and instruments made in connection with the treaty's conclusion. These materials are legally distinct from the supplementary means addressed in Article 32.
Object and purpose are important but not self-executing. They help orient interpretation within the treaty's legal design. They do not authorize an interpreter to replace agreed language with a broader policy objective or to impose an obligation that the text cannot reasonably bear.
The integrated character of Article 31 is particularly significant in disputes where one party relies heavily on a dictionary definition while another relies on institutional purpose. Neither approach alone reflects the Convention's method. The legal meaning emerges from the combined interpretive elements applicable to the provision.
9.2 Subsequent agreements and subsequent practice
Article 31(3) requires account to be taken, together with context, of subsequent agreements between the parties regarding interpretation or application, subsequent practice establishing the agreement of the parties regarding interpretation, and relevant rules of international law applicable in relations between the parties (United Nations, 1969, art. 31(3)).
Subsequent practice can be important because treaty implementation may reveal how the parties understand the agreement after its conclusion. The threshold in Article 31(3)(b), however, is not satisfied merely because conduct has occurred repeatedly. The practice must establish agreement of the parties regarding interpretation.
The ICJ's judgment in Kasikili/Sedudu Island illustrates the distinction. The Court considered subsequent conduct but found that the evidence relied upon did not establish the parties' agreement concerning interpretation at the level required by the applicable rule (ICJ, 1999).
The ILC's 2018 conclusions on subsequent agreements and subsequent practice provide detailed guidance on these concepts. The conclusions are non-binding, but they are useful in distinguishing interpretive practice from conduct that may be relevant for other reasons without demonstrating an agreed interpretation (International Law Commission, 2018).
Institutional practice may also be relevant in certain treaty regimes. Its legal weight depends on the constituent treaty, the competence of the institution, the conduct of the parties, and the basis on which the practice is invoked. Institutional repetition does not automatically amount to agreement of all treaty parties.
9.3 Supplementary means and multilingual texts
Article 32 permits recourse to supplementary means of interpretation, including preparatory work and the circumstances of conclusion. Those means may confirm the result reached under Article 31 or assist where interpretation under Article 31 leaves the meaning ambiguous or obscure or produces a manifestly absurd or unreasonable result (United Nations, 1969, art. 32).
Preparatory work can reveal how wording developed, what proposals were rejected, or which legal problems negotiators were attempting to address. It must be used carefully. Statements by individual delegations do not automatically establish the common intention of all parties, and negotiating records may be incomplete.
Article 33 addresses treaties authenticated in two or more languages. Unless the treaty provides or the parties agree that one text will prevail, each authenticated language version is equally authoritative (United Nations, 1969, art. 33).
Where comparison reveals a difference that Articles 31 and 32 do not remove, Article 33 requires adoption of the meaning that best reconciles the texts, having regard to the treaty's object and purpose. Multilingual interpretation therefore begins from equality of authentic texts rather than a presumption that one language supplies the controlling meaning.
10. Treaties and Third States
Article 34 expresses the general rule that a treaty does not create obligations or rights for a third State without its consent. The principle reflects the consensual structure of treaty law. States cannot ordinarily impose treaty obligations on another State merely by concluding an agreement between themselves (United Nations, 1969, art. 34).
Article 35 permits creation of an obligation for a third State where the parties to the treaty intend the provision to establish that obligation and the third State expressly accepts it in writing. The requirement of express written acceptance provides a strong safeguard for third-State consent.
Article 36 treats rights differently. A treaty may confer a right on a third State where the parties intend the provision to accord that right and the third State assents. Assent is presumed while the contrary is not indicated unless the treaty provides otherwise.
The rules concern rights and obligations arising from the treaty as such. They do not prevent the substantive rule stated in a treaty from existing independently through another source of international law.
Article 38 makes that point explicit. Nothing in Articles 34–37 prevents a rule set forth in a treaty from becoming binding upon a third State as a customary rule of international law recognized as such (United Nations, 1969, art. 38).
A non-party is thus not bound by a VCLT provision merely because it appears in an influential multilateral convention. If the same rule binds the State through custom, the source of the obligation is customary international law. Identical substantive rules may operate through legally distinct sources.
11. Amendment and Inter Se Modification
Treaties require mechanisms that allow States to change legal arrangements without destroying their stability. Articles 39–41 distinguish amendment of a treaty from modification of its operation between only certain parties.
Article 39 states the general rule that a treaty may be amended by agreement between the parties. The ordinary VCLT rules concerning conclusion and entry into force apply to the amending agreement unless the treaty provides otherwise (United Nations, 1969, art. 39).
The original treaty may itself prescribe amendment procedures, voting requirements, entry-into-force thresholds, or institutional mechanisms. Those clauses take priority within the legal relationship they create and may produce different amendment structures across treaty regimes.
Article 40 addresses amendment of multilateral treaties. A proposal to amend the treaty as between all parties must generally be notified to all contracting States, which are entitled to participate in decisions concerning the proposal and in negotiation and conclusion of the amending agreement.
An amending agreement does not automatically bind a party to the original treaty that does not become a party to the amendment. Multilateral legal relations may therefore become differentiated, with the amended treaty governing some relationships and the original version continuing to govern others.
Article 41 concerns modification between certain parties only. Such an inter se modification may be permissible where the treaty provides for it or where it is not prohibited, provided the modification does not affect other parties' rights or obligations and does not concern a provision whose derogation would be incompatible with effective execution of the treaty's object and purpose as a whole (United Nations, 1969, art. 41).
12. Invalidity and Defects of Consent
Invalidity concerns the legal basis on which a treaty or a State's consent can stand. It should be distinguished from breach. A State may violate a valid treaty without the treaty becoming invalid, while a valid ground of invalidity concerns the status of consent or of the treaty itself.
Part V restricts the available grounds deliberately. Article 42 provides that the validity of a treaty or of State consent may be impeached only through application of the Convention. The same Part also governs termination, denunciation, withdrawal, and suspension (United Nations, 1969, art. 42).
Articles 44 and 45 further protect legal stability. Article 44 addresses separability of treaty provisions in defined circumstances. Article 45 prevents a State from invoking certain grounds after it has expressly agreed that the treaty is valid or remains in force, or where its conduct requires it to be considered as having acquiesced.
Political dissatisfaction, economic disadvantage, or a change of government is not enough. A State challenging treaty validity must identify a recognized legal ground and comply with the procedural framework applicable to the claim.
12.1 Error, fraud, corruption, coercion, and internal law
Article 46 permits a State to invoke violation of its internal law concerning competence to conclude treaties only where the violation was manifest and concerned a rule of fundamental importance. A violation is manifest when it would be objectively evident to any State conducting itself in the matter according to normal practice and in good faith (United Nations, 1969, art. 46).
Articles 48–50 address error, fraud, and corruption. Error may be invoked where it relates to a fact or situation assumed to exist when the treaty was concluded and that assumption formed an essential basis of consent, subject to limitations where the State contributed to the error or circumstances should have put it on notice. Fraud concerns inducement through fraudulent conduct by another negotiating State, while Article 50 concerns corruption of a representative.
Article 51 provides that an expression of consent procured through coercion of a State representative by acts or threats directed against that person has no legal effect. Article 52 concerns coercion of the State itself and declares a treaty void where its conclusion was procured by the threat or use of force in violation of the principles of international law embodied in the UN Charter (United Nations, 1969, arts 51–52).
The diplomatic conference separately adopted a Declaration on the Prohibition of Military, Political or Economic Coercion in the Conclusion of Treaties. The Declaration condemned such coercion but was not incorporated into the operative text of Article 52. The legal scope of Article 52 should therefore not be expanded simply by treating every form of political or economic pressure in negotiations as equivalent to the prohibited threat or use of force.
The distinction is important because treaty negotiations frequently involve bargaining, economic leverage, and political pressure. Whether particular conduct violates another rule of international law is a separate inquiry. Article 52 has a specific legal formulation and should be applied according to that formulation rather than through an undefined concept of unequal bargaining power.
12.2 Jus cogens and invalid treaties
Article 53 addresses a qualitatively different limitation on treaty validity. A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law. The Convention defines such a norm as one accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which may be modified only by a subsequent norm having the same character (United Nations, 1969, art. 53).
The category is exceptional. A rule does not become jus cogens merely because it is important, widely ratified, morally compelling, or frequently described as fundamental. Peremptory status requires the specific acceptance and recognition demanded by general international law.
The International Law Commission adopted non-binding draft conclusions on identification and legal consequences of peremptory norms in 2022. They distinguish identification of a norm of general international law from the further requirement that the international community of States as a whole accept and recognize its peremptory character (International Law Commission, 2022).
The draft conclusions provide a structured methodology and detailed commentary, but they do not themselves create treaty obligations or transform disputed propositions into binding jus cogens. Their legal significance lies in codification work, synthesis of authority, and guidance concerning the identification process.
Article 71 addresses consequences where a treaty is void under Article 53. Parties must eliminate as far as possible the consequences of acts performed in reliance on provisions conflicting with the peremptory norm and bring their mutual relations into conformity with that norm. The effect demonstrates that jus cogens limits what States can accomplish through consent alone.
13. Termination, Withdrawal, and Suspension
The VCLT permits treaty relations to end or change through legally recognized mechanisms. A treaty may terminate according to its own provisions, by consent, through withdrawal where permitted, or on one of the limited grounds identified in Part V.
Termination ordinarily ends the operation of the treaty for the future. Withdrawal or denunciation concerns departure of a particular party where the treaty structure allows it. Suspension leaves the treaty in existence while temporarily stopping the operation of specified provisions or obligations in the relevant relationship.
These mechanisms should not be confused with breach. An unlawful refusal to perform a treaty does not automatically terminate it. Nor does the existence of an internationally wrongful act necessarily establish one of the VCLT grounds for ending the treaty relationship.
The distinction was central in Gabčíkovo-Nagymaros Project. The ICJ examined Hungary's attempts to terminate a 1977 treaty under the law of treaties while also distinguishing questions concerning responsibility for internationally wrongful conduct (ICJ, 1997).
13.1 Treaty terms, consent, breach, and impossibility
Article 54 permits termination or withdrawal in accordance with the treaty's provisions or at any time by consent of all parties after consultation with the other contracting States. Express exit clauses are therefore the first place to look when assessing whether unilateral withdrawal is available (United Nations, 1969, art. 54).
Article 56 addresses treaties containing no provision regarding termination, denunciation, or withdrawal. Such a treaty is not subject to denunciation or withdrawal unless it is established that the parties intended to admit that possibility or a right can be implied from the treaty's nature. The Article also requires at least 12 months' notice of an intention to denounce or withdraw.
Article 60 regulates material breach. In a bilateral treaty, a material breach by one party entitles the other to invoke the breach as a ground for terminating the treaty or suspending its operation. The rules for multilateral treaties are more differentiated because a breach may affect the parties in different ways.
Article 60(5) creates an important limitation. The provisions on material breach do not apply to provisions relating to protection of the human person contained in treaties of a humanitarian character, particularly provisions prohibiting reprisals against persons protected by those treaties (United Nations, 1969, art. 60(5)).
Article 61 deals with supervening impossibility of performance. It may be invoked when the impossibility results from permanent disappearance or destruction of an object indispensable for execution of the treaty. Temporary impossibility may support suspension rather than termination. A State cannot rely on the ground where the impossibility results from its own breach of the treaty or another international obligation owed to a treaty party.
13.2 Fundamental change and new jus cogens
Article 62 recognizes fundamental change of circumstances only under restrictive conditions. The circumstances that existed when the treaty was concluded must have constituted an essential basis of consent, the change must have been unforeseen, and its effect must radically transform the extent of obligations still to be performed (United Nations, 1969, art. 62).
The ground cannot be invoked for a treaty establishing a boundary. It is also unavailable where the fundamental change results from a breach by the invoking party of the treaty or another international obligation owed to another treaty party.
In Gabčíkovo-Nagymaros Project, Hungary relied on changes including political, economic, and environmental developments. The ICJ did not accept that the strict conditions required to terminate the treaty on the basis of fundamental change had been satisfied (ICJ, 1997).
The judgment illustrates the exceptional nature of Article 62. Long-term treaties inevitably operate in changing political and economic conditions. If ordinary change were sufficient, the stability promised by pacta sunt servanda would be significantly weakened.
Article 64 deals with a different development. Where a new peremptory norm of general international law emerges and an existing treaty conflicts with it, the treaty becomes void and terminates. Article 53 concerns jus cogens existing when a treaty is concluded; Article 64 addresses a peremptory norm that emerges later (United Nations, 1969, arts 53 and 64).
14. Depositaries, Notifications, and Registration
Multilateral treaties depend on reliable administration. Instruments of ratification and accession must be received, reservations and objections circulated, corrections recorded, notifications transmitted, and the status of participation maintained accurately.
Articles 76 and 77 regulate depositaries and their functions. A depositary may be one or more States, an international organization, or the chief administrative officer of an organization, depending on the treaty. Its responsibilities include custody of the original text and full powers, preparation of certified copies, receipt of signatures and instruments, examination of formal requirements, transmission of information to parties, and registration where appropriate (United Nations, 1969, arts 76–77).
Article 76 provides that depositary functions are international in character and that the depositary must act impartially. This requirement is important when political disagreements arise concerning reservations, credentials, notifications, or other treaty actions.
The United Nations Treaty Handbook describes the depositary role primarily as administrative and procedural. A depositary may examine whether an instrument appears to meet formal requirements and notify States of issues, but it is not generally a tribunal empowered to resolve every substantive dispute concerning the legal validity of a treaty action (United Nations Treaty Section, 2012).
Article 80 requires treaties, after entry into force, to be transmitted to the UN Secretariat for registration or filing and recording, as appropriate, and for publication. The registration regime also rests on Article 102 of the UN Charter (United Nations, 1945, art. 102; United Nations, 1969, art. 80).
Failure to register does not make a treaty invalid. Article 102(2) provides, however, that no party to an unregistered treaty or international agreement may invoke that treaty or agreement before any organ of the United Nations. The restriction applies to the parties to the unregistered agreement and is not limited to whichever party was practically responsible for arranging registration.
15. Customary Law and States Outside the VCLT
The VCLT operates within a legal system in which treaty rules and customary rules may coexist. A State party is bound by applicable VCLT provisions because it has consented to the Convention. A State outside that treaty relationship may nevertheless be bound by a corresponding rule if the rule independently forms part of customary international law.
Article 4 makes the distinction especially clear. The Convention itself applies only to treaties concluded by States after the VCLT has entered into force for those States, without prejudice to the application of rules contained in the Convention to which treaties would be subject under international law independently of the Convention (United Nations, 1969, art. 4).
The provision preserves the customary law that existed before the VCLT and any customary rules subsequently recognized. It also explains why courts can use particular VCLT rules in relation to older treaties without applying the Convention retroactively as a treaty.
In Kasikili/Sedudu Island, the ICJ applied customary rules of interpretation reflected in the VCLT to an agreement dating from 1890. In Gabčíkovo-Nagymaros Project, the Court considered customary rules corresponding to VCLT provisions in relation to a 1977 treaty that fell outside the Convention's direct temporal application between the parties (ICJ, 1997; ICJ, 1999).
The customary status of a particular provision must still be established rather than presumed. Some VCLT rules are widely recognized as codifications of custom. Other provisions contain detailed procedural arrangements, treaty-specific mechanisms, or elements of progressive development whose customary status cannot simply be assumed.
The distinction has practical consequences for legal pleading. Saying that “the VCLT applies” may obscure the true legal basis. A more accurate argument identifies the specific VCLT rule, explains whether the Convention applies as treaty law, and, where necessary, establishes the corresponding customary rule independently.
16. Scope Limits and Related Treaty Regimes
Article 1 confines the direct scope of the 1969 Convention to treaties between States. Article 3 prevents that limitation from being misunderstood as a declaration that other international agreements lack legal force (United Nations, 1969, arts 1 and 3).
Treaties involving international organizations were addressed in the 1986 Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations. That instrument follows much of the structure of the 1969 Convention but is a separate treaty. As of 26 August 2026, it has not entered into force (United Nations, 1986; United Nations Treaty Collection, 2026b).
The absence of entry into force does not make the 1986 text legally irrelevant. Individual rules may reflect customary international law independently, and the Convention remains an important product of ILC codification and diplomatic negotiation. Its provisions should nevertheless not be presented as binding treaty law for States and organizations merely because they parallel the 1969 VCLT.
Article 73 of the 1969 Convention also preserves questions arising from State succession, international responsibility, and the outbreak of hostilities. State succession in respect of treaties became the subject of the 1978 Vienna Convention on Succession of States in Respect of Treaties, which entered into force in 1996 but has substantially narrower participation than the 1969 VCLT (United Nations, 1978).
The effects of armed conflict on treaties were later examined by the International Law Commission. In 2011, the ILC adopted Draft Articles on the Effects of Armed Conflicts on Treaties with commentaries. Those articles are non-binding ILC work rather than a multilateral convention in force (International Law Commission, 2011b).
International responsibility presents another boundary. The VCLT may determine whether a treaty remains valid or whether a ground for termination exists. The legal consequences of breaching an obligation while the treaty remains in force belong principally to the law of international responsibility.
These boundaries strengthen rather than weaken the VCLT's usefulness. The Convention provides a general law of treaties, but responsible legal analysis must identify where that general framework ends and another treaty, customary rule, institutional regime, or field of international law becomes controlling.
17. Recommended Study Guide
The VCLT provides a general legal framework, but practical treaty work often requires a more detailed method. Questions about legal status, full powers, reservations, entry into force, interpretation, amendment, suspension, withdrawal, and termination can arise together in the same instrument.
Treaty Law in Practice: Formation, Interpretation, Reservations and Withdrawal develops those subjects as a dedicated treaty-law study guide. It addresses treaty formation, Articles 31–33 interpretation, reservations and objections, final clauses, withdrawal, and related analytical methods.
The guide is most relevant to readers who need to move from a general understanding of the Vienna Convention to structured treaty analysis. That includes advanced students as well as lawyers, researchers, diplomats, government advisers, and professionals working with international agreements.
It should be treated as supplementary study material rather than as legal authority. Primary treaty texts, official treaty-status records, judgments, and other applicable sources remain controlling where a legal proposition or current participation status must be established.
Also read
Conclusion
The Vienna Convention on the Law of Treaties provides the principal general framework for written treaties between States. Its rules organize how consent is expressed, how treaties become operative, how reservations affect multilateral relationships, how treaty terms are interpreted, and under what conditions obligations may be amended, challenged, suspended, or brought to an end.
Several of its best-known provisions express ideas that reach beyond the Convention's formal membership. Pacta sunt servanda, the interpretive rules associated with Articles 31 and 32, and parts of the law concerning termination have been recognized in international practice and jurisprudence as reflecting customary international law. That wider operation depends on the customary character of the specific rule, not on a presumption that the Convention binds every State in its entirety.
The VCLT also places limits on consent. Article 53 makes treaties conflicting with existing peremptory norms void, while Article 64 deals with the emergence of new jus cogens. At the same time, the Convention protects treaty stability by restricting the grounds on which States may invoke internal law, error, coercion, fundamental change, breach, or impossibility to escape obligations.
Its legal importance is clearest when those principles are applied with precision. Treaty law distinguishes signature from ratification, political commitment from legal agreement, breach from invalidity, treaty obligation from custom, and general VCLT rules from treaty-specific regimes. Those distinctions explain why the Convention remains central to international legal practice more than half a century after its adoption.
References
Human Rights Committee (1994) ‘General Comment No. 24: Issues relating to reservations made upon ratification or accession to the Covenant or the Optional Protocols thereto, or in relation to declarations under Article 41 of the Covenant’. CCPR/C/21/Rev.1/Add.6.
International Court of Justice (1951) Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide, Advisory Opinion, ICJ Reports 1951, p. 15.
International Court of Justice (1974) Nuclear Tests (Australia v France), Judgment, ICJ Reports 1974, p. 253.
International Court of Justice (1994) Maritime Delimitation and Territorial Questions between Qatar and Bahrain (Qatar v Bahrain), Jurisdiction and Admissibility, Judgment, ICJ Reports 1994, p. 112.
International Court of Justice (1997) Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Judgment, ICJ Reports 1997, p. 7.
International Court of Justice (1999) Kasikili/Sedudu Island (Botswana/Namibia), Judgment, ICJ Reports 1999, p. 1045.
International Law Commission (1966) ‘Draft Articles on the Law of Treaties with Commentaries’, Yearbook of the International Law Commission, 1966, vol. II, pp. 187–274.
International Law Commission (2011a) Guide to Practice on Reservations to Treaties, with Commentaries. Report of the International Law Commission, Sixty-third Session, A/66/10/Add.1.
International Law Commission (2011b) ‘Draft Articles on the Effects of Armed Conflicts on Treaties, with Commentaries’, Yearbook of the International Law Commission, 2011, vol. II, Part Two.
International Law Commission (2018) ‘Draft Conclusions on Subsequent Agreements and Subsequent Practice in Relation to the Interpretation of Treaties, with Commentaries’, Yearbook of the International Law Commission, 2018, vol. II, Part Two.
International Law Commission (2021) ‘Guide to Provisional Application of Treaties, with Commentaries’, Report of the International Law Commission, Seventy-second Session, A/76/10.
International Law Commission (2022) ‘Draft Conclusions on Identification and Legal Consequences of Peremptory Norms of General International Law (Jus Cogens), with Commentaries’, Report of the International Law Commission, Seventy-third Session, A/77/10.
United Nations (1945) Charter of the United Nations. Signed 26 June 1945; entered into force 24 October 1945.
United Nations (1969) Vienna Convention on the Law of Treaties. Adopted 22 May 1969; opened for signature 23 May 1969; entered into force 27 January 1980, 1155 UNTS 331.
United Nations (1978) Vienna Convention on Succession of States in Respect of Treaties. Adopted 23 August 1978; entered into force 6 November 1996, 1946 UNTS 3.
United Nations (1986) Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations. Adopted 21 March 1986; not yet in force as of 26 August 2026.
United Nations Treaty Collection (2026a) ‘Vienna Convention on the Law of Treaties: Status of Participation’. Chapter XXIII, No. 1. Status checked 26 August 2026.
United Nations Treaty Collection (2026b) ‘Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations: Status of Participation’. Chapter XXIII, No. 3. Status checked 26 August 2026.
United Nations Treaty Section (2012) Treaty Handbook. Revised edition. New York: United Nations.
Zemanek, K. (2009) ‘Vienna Convention on the Law of Treaties: Introductory Note’. United Nations Audiovisual Library of International Law.
