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Definition and classification


Formation Amendment and Termination



The formal legal device for making changes to the text of a bilateral or multilateral trade agreement in the form of a treaty (as distinct from a non-legally binding MOU / political commitment), whether to its core provisions or to annexes or appendices, is an amendment.

If the changes apply only among a subset of treaty parties, they are referred to as ‘modifications’.

Where a bilateral treaty provides for the procedure for adopting an amendment to be determined by the parties, the agreement to amend coming into effect when formally confirmed by an exchange of notes, the amendment will often be recorded first in an MOU, which may also provide for the amendment to be put into effect ‘administratively’ pending confirmation.

Article 39 of the Vienna Convention on the Law of Treaties (General rule regarding the amendment of treaties) states,

‘A treaty may be amended by agreement between the parties. The rules laid down in Part II apply to such an agreement except in so far as the treaty may otherwise provide.’

This applies whether a treaty is bilateral or multilateral.

The use of the word ‘agreement’ recognises that a treaty can be amended by an agreement that is not a treaty, or possibly an oral agreement, the legal force of which is preserved by Article 3.

Article 31(3)(a) states, ‘There shall be taken into account, together with the context:

(a)    any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions’

Therefore a treaty can also be effectively amended by a subsequent agreement between the parties regarding the interpretation or application of the treaty.

Article 39 provides that the rules laid down in Part II (Conclusion and Entry into Force of Treaties) apply to an agreement to amend a treaty “except insofar as the treaty may otherwise provide.” This phrase recognises that many treaties, especially multilateral, now have built-in amendment mechanisms. It is wrong to think that the Vienna Convention is a rigid structure which places obstacles in the way of treaty modification; rather it allows states to include in treaties such amendment provisions (good or bad) as they wish or, indeed, nothing at all.

Sometimes the amendments are so numerous or extensive that it may be better to replace the whole of the original treaty with a new one. Alternatively, a consolidated text showing the treaty as amended should be agreed and produced for information. If the amendments have the effect of replacing the original treaty and any previous amendments to it, another way is to require any party to the amendment treaty to denounce all the previous treaties with effect from the date the new treaty enters into effect for that party. The replacement treaty may provide that its entry into force for a party shall be deemed to amount to denunciation of the original treaty.’

Modern Treaty Law and Practice by Anthony Aust (2013), pages 233 and 238.

In addition to the broadly framed general principle contained in Article 39, Articles 40 and 41 contain residual procedural rules intended to guide the amendment of multilateral treaties.

Article 40 (Amendment of multilateral treaties) states,

‘1.    Unless the treaty otherwise provides, the amendment of multilateral treaties shall be governed by the following paragraphs.

  1.      Any proposal to amend a multilateral treaty as between all the parties must be notified to all the contracting States, each one of which shall have the right to take part in:

(a)    the decision as to the action to be taken in regard to such proposal;

(b)    the negotiation and conclusion of any agreement for the amendment of the treaty.

  1.      Every State entitled to become a party to the treaty shall also be entitled to become a party to the treaty as amended.
  2.      The amending agreement does not bind any State already a party to the treaty which does not become a party to the amending agreement; article 30, paragraph 4(b), applies in relation to such State.
  3.      Any State which becomes a party to the treaty after the entry into force of the amending agreement shall, failing an expression of a different intention by that State:

(a)    be considered as a party to the treaty as amended; and

(b)    be considered as a party to the unamended treaty in relation to any party to the treaty not bound by the amending agreement.’

Article 41 (Agreements to modify multilateral treaties between certain of the parties only) states,

‘1.    Two or more of the parties to a multilateral treaty may conclude an agreement to modify the treaty as between themselves alone if:

(a)    the possibility of such a modification is provided for by the treaty; or

(b)    the modification in question is not prohibited by the treaty and:

(i)      does not affect the enjoyment by the other parties of their rights under the treaty or the performance of their obligations;

(ii)     does not relate to a provision, derogation from which is incompatible with the effective execution of the object and purpose of the treaty as a whole.

  1.      Unless in a case falling under paragraph 1(a) the treaty otherwise provides, the parties in question shall notify the other parties of their intention to conclude the agreement and of the modification to the treaty for which it provides.’

As these residual rules confirm, amendments require agreement between treaty parties, but not necessarily between all parties. For bilateral treaties, of course, the agreement of both parties is needed to effect any changes. The main question here concerns the form in which the parties’ agreement is to be expressed. Some bilateral treaties stipulate that written agreements, for example though exchange of notes, is required. It is worth noting that for plurilateral treaties too the unanimity rule continues to hold sway. For example, the North American Free Trade Agreement (NAFTA) between Canada, Mexico, and the United States stipulates that the “Parties may agree on any modification of or addition to” NAFTA.

For multilateral treaties, the default rule is that amendments must be proposed and adopted, and that individual parties then decide whether or not they wish to become a party to the amendment. However, parties are free to reach informal agreements on the amendment, and to decide on the details of the amendment process. This open-endedness of the residual rules reflects not only… variations in State practice, but also the fact that international law does not contain an acte contraire principle. In other words, there is no general legal requirement that changes to a treaty be made through the same process or by an act of the same legal nature as the original instrument. When a party joins a treaty for which an amendment is already in force, it will normally be bound by the amendment unless it indicates otherwise. If two or more parties wish to change a treaty between themselves – as opposed to between all parties – they can do so, subject to certain limitations, by way of a modification.’ The Oxford Guide to Treaties (2012) edited by Duncan B. Hollis.


Part V of the Vienna Convention on the Law of Treaties (the ‘Convention’) sets out the various circumstances in which a treaty can be denounced, terminated or its operation suspended, other than on grounds of invalidity.

‘Denunciation and withdrawal are used interchangeably to refer to a unilateral act by which a nation that is currently a party to a treaty ends its membership in that treaty. In the case of multilateral agreements, denunciation or withdrawal generally does not affect the treaty’s continuation in force for the remaining parties. For bilateral agreements, in contrast, denunciation or withdrawal by either party results in termination of the treaty for both parties. The termination of a multilateral agreement occurs when the treaty ceases to exist for all States parties.’ The Oxford Guide to Treaties edited by Duncan B.Hollis (‘Hollis’), page 635.

‘To be effective, denunciation, termination or suspension may take place only as a result of the application of the provisions of the treaty itself or Article 42(2) [of the Convention]. These days, most treaties contain provisions on duration and termination, often in the same article. But when there are none, one must consider not only the relevant article in Part V [of the Convention], but other articles in that Part which govern the conditions for applying the article, such as Articles 65-68 concerning the procedure to be followed. Certain other articles of the Convention may also be relevant…’ Modern Treaty Law and Practice by Anthony Aust, 3rd Edition, page 245.

Article 42(2) provides, ‘The termination of a treaty, its denunciation or the withdrawal of a party, may take place only as a result of the application of the provisions of the treaty or of the present Convention. The same rule applies to suspension of the operation of a treaty.’

The design and operation of treaty exit clauses is governed by the foundational principle of State consent.

Article 54 of the Convention provides,

‘The termination of a treaty or the withdrawal of a party may take place:

(a)     In conformity with the provisions of the treaty; or

(b)     At any time by consent of all the parties after consultation with the other contracting States’.

‘At the negotiation stage, State representatives have free rein to choose the substantive and procedural rules that will govern the future cessation of their relationship. Once those rules have been adopted as part of a final text, however, a State that ratifies or accedes to the treaty also accepts any conditions or restrictions on termination, withdrawal or denunciation that the treaty contains. Unilateral exit attempts that do not comply with these conditions or restrictions are ineffective. A state that ceases performance after such an attempt remains a party to the treaty, albeit one that may be in breach of its obligations. However, the treaty parties may waive these conditions or restrictions and permit unilateral withdrawal, or terminate the treaty, “at any time by consent of all the parties after consultation with the other contracting states.”… States are the undisputed masters of treaty exit rules… But what if a treaty omits such clauses entirely? In such a situation the VCLT provides default rules to govern the end of the parties’ relationship.’ Hollis page 636.

Article 56 provides,

‘1.    A treaty which contains no provision regarding its termination and which does not provide for denunciation or withdrawal is not subject to denunciation or withdrawal unless:

(a)    it is established that the parties intended to admit the possibility of denunciation or withdrawal; or

(b)    a right of denunciation or withdrawal may be implied by the nature of the treaty.

  1. A party shall give not less than twelve months’ notice of its intention to denounce or withdraw from a treaty under paragraph 1.’

Whilst the commercial character of a treaty is not determinative, in principle, a trade agreement is likely to fall within the Article 56(1)(b) exception.

Article 70 further provides,

‘1.    Unless the treaty otherwise provides or the parties otherwise agree, the termination of a treaty under its provisions or in accordance with the present Convention:

(a)    releases the parties from any obligation further to perform the treaty;

(b)    does not affect any right, obligation or legal situation of the parties created through the execution of the treaty prior to its termination.

  1. If a State denounces or withdraws from a multilateral treaty, paragraph 1 applies in the relations between that State and each of the other parties to the treaty from the date when such denunciation or withdrawal takes effect.’

‘Taken together, these provisions restrict States from using exit to avoid accountability for past violations of international law. They also discourage the precipitous and opportunistic withdrawals in which a State seeks to exit and then immediately violate a rule that it previously accepted as binding.’ Hollis, page 641.

Article 43 also provides, ‘The invalidity, termination or denunciation of a treaty, the withdrawal of a party from it, or the suspension of its operation, as a result of the application of the present Convention or of the provisions of the treaty, shall not in any way impair the duty of any State to fulfil any obligation embodied in the treaty to which it would be subject under international law independently of the treaty.’

Treaty exit clauses operate in tandem with other flexibility devices including: reservations; amendment rules; escape clauses; and renegotiation provisions, that treaty makers use to manage risk.



Model Clauses


Research Resources

Vienna Convention