A State that accepts most of a treaty but not one provision can still join it, by formulating a reservation that modifies that provision for itself alone. Articles 19 to 23 of the Vienna Convention on the Law of Treaties, 1969 govern reservations to treaties from formulation to withdrawal.
The cost of a reservation falls on the other parties to the treaty, and an international court will give effect to it even where the allegations are grave. In Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Rwanda), the Democratic Republic of the Congo asked the International Court of Justice to hear allegations of genocide against Rwanda. Rwanda had acceded to the Genocide Convention with a reservation to Article IX, the clause under which disputes about that Convention reach the Court, and in 2006 the Court held by 15 votes to 2 that it had no jurisdiction to hear them.
Rules that produce that result exist because the alternative is a smaller treaty. Before 1951, a reservation took effect only if every other party accepted it, so a single objection kept the reserving State outside the convention altogether. Articles 19 to 23 let a State that cannot accept one provision join on the rest, which leaves the other parties with a State bound by most of the treaty rather than none of it.
What those Articles do not supply is anyone to apply them. Article 19 of the Vienna Convention on the Law of Treaties, 1969 states the test a reservation must pass, and Article 20 then gives the assessment to each other party separately, so no organ rules on permissibility for everybody. One reservation can therefore produce a different treaty relationship with every State on the list.
Treaty drafters have answered that difficulty by writing the reservations rule into the treaty itself, and the most recent treaty to take that route came into force in January 2026. The Agreement under the Law of the Sea Convention on marine biological diversity of areas beyond national jurisdiction, the BBNJ Agreement, carries Article 70, under which no reservations or exceptions may be made unless another article expressly permits them. More than twenty States and the European Union have filed declarations or exceptions under it even so, and Norway has declared that it does not consider itself bound by the declarations other States make and reserves the right to take a position on them at any time.
Reservations to treaties permitted under Article 19
A State may formulate a reservation to any treaty unless one of three things listed in Article 19 stops it, and Article 70 of the BBNJ Agreement is an instance of the first of them. The default in the Vienna Convention is permission, so a reservation needs nobody’s leave and no stated justification.
What counts as a reservation is settled by Article 2(1)(d), which defines it as a unilateral statement, however phrased or named, made by a State when signing, ratifying, accepting, approving or acceding to a treaty, by which it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State. Under the words “however phrased or named”, a State that calls its statement an interpretative declaration has not thereby made one, and every other party is entitled to read the statement’s substance instead of its label.
Whether the three bars leave a ratifying State any room is easiest to follow on one set of facts. A State is preparing to ratify a multilateral human rights convention. Its law ministry accepts every substantive obligation in the text, and it will not accept the clause referring disputes about the convention to the International Court of Justice.
Everything then turns on what the convention itself says about reservations. If the convention carries a clause in the form of Article 70 of the BBNJ Agreement, the ministry has no route at all, and it must either ratify with the dispute clause or stay outside the convention. If the convention says nothing about reservations, which is the position under most human rights conventions, the ministry reaches the third bar, and the question becomes whether excluding the dispute clause is incompatible with the object and purpose of the convention.
Two things follow on that record. The reservation is permissible, because a clause about where disputes go is not the object the convention was made to achieve, and that is the answer the International Court of Justice gave on comparable facts in 2006. The other parties are not bound to accept it, and each of them decides separately what to do about it, which is the subject of Article 20.
Treaties that bar reservations outright
A treaty bars reservations outright by saying so, and two of the most widely ratified instruments in force say so in the same words. Article 309 of the United Nations Convention on the Law of the Sea, 1982 provides that no reservations or exceptions may be made to the Convention unless expressly permitted by other articles of it. Article 70 of the BBNJ Agreement, which entered into force on 17 January 2026, reproduces that sentence exactly.
The closing words of both articles are the Article 19(b) route in operation. Article 10 of the BBNJ Agreement applies the Agreement to marine genetic resources collected after it enters into force for a Party, and extends it to resources collected earlier unless that Party makes an exception in writing under Article 70. Roughly twenty States took that exception when they ratified, among them China, France, Japan, the Republic of Korea, Spain and the United Kingdom. Article 71 leaves a Party the alternative of filing a declaration, provided the declaration does not purport to exclude or to modify the legal effect of the Agreement’s provisions in their application to that Party.
The opposite default appears in the WHO Pandemic Agreement, adopted by the World Health Assembly in May 2025. Its Article 25 provides that reservations may be made unless incompatible with the object and purpose of the Agreement, which writes the Article 19(c) test into the treaty itself. That Agreement opens for signature only once the annex required by its Article 12 has been adopted, and the negotiations on the annex ran past the May 2026 deadline, so no reservation has yet been made to it.
The object and purpose test for reservations under Article 19(c)
Article 19(c) applies where the treaty is silent, and it asks whether the reservation is incompatible with the object and purpose of the treaty. The International Court of Justice supplied that test in its Advisory Opinion of 28 May 1951 on reservations to the Genocide Convention, years before the Vienna Convention adopted it. The Court held that a State whose reservation has been objected to by some parties and not by others may be regarded as a party if the reservation is compatible with the object and purpose of the convention, and that a State cannot be bound by a reservation to which it has not consented.
Each State applies the test for itself. The Court answered a question put to it by the General Assembly and named no organ to apply the test afterwards, so compatibility under the law of treaties is assessed by every other party separately and nowhere centrally.
The International Court of Justice fixed how far the test reaches for one recurring class of reservation in 2006. In Armed Activities on the Territory of the Congo, the Democratic Republic of the Congo argued that Rwanda’s reservation to Article IX of the Genocide Convention was incompatible with the Convention’s object and purpose. The Court rejected the argument, holding that a reservation to the clause conferring jurisdiction does not go to the substantive obligations the Convention imposes, and it found that it had no jurisdiction by 15 votes to 2.
Acceptance of and objection to reservations under Article 20
Because Article 19 names nobody to apply its test, Article 20 gives the decision to each other contracting State separately, and each of them may accept the reservation or object to it. Acceptance under Article 20(4)(a) constitutes the reserving State a party in relation to the State that accepted, if and when the treaty is in force between them. Under Article 20(4)(c), an act expressing consent to be bound and containing a reservation takes effect as soon as at least one other contracting State has accepted the reservation, so a single acceptance is enough to make the reserving State a party to somebody.
Three situations are taken out of that scheme before it starts. A reservation expressly authorised by the treaty needs no subsequent acceptance under Article 20(1). Where the limited number of negotiating States and the object and purpose of a treaty show that applying it in its entirety between all the parties was an essential condition of each State’s consent, Article 20(2) requires acceptance by all the parties. A reservation to the constituent instrument of an international organisation requires the acceptance of that organisation’s competent organ under Article 20(3).
The twelve-month clock for objecting to reservations
A State that says nothing about a reservation has accepted it. Article 20(5) treats a reservation as accepted by a State if that State has raised no objection to it by the end of twelve months after being notified of it, or by the date on which it expressed its consent to be bound by the treaty, whichever is later. The period runs from notification, which is why Article 23 requires the reservation to be communicated in the first place.
The second limb of that rule applies to a State joining a treaty that already carries reservations. A State acceding in 2026 to a convention that has carried reservations since the 1980s has until the date it deposits its own instrument to object to any of them.
It does not inherit the silence of the States that were already parties, and nothing it files after that date operates as an objection. On the day its consent takes effect, it has accepted every reservation on the register that it did not answer.
Most reservations are accepted in this way, by silence rather than by a decision. A State that has let the twelve months run cannot object afterwards, and it is then in the position Article 21 describes for a State that has accepted.
The two kinds of objection to reservations under Article 20(4)(b)
An objection does not by itself stop the treaty coming into force between the objecting State and the reserving State. Article 20(4)(b) gives it that effect only where a contrary intention is definitely expressed by the objecting State. There are therefore two kinds of objection, and what separates them is a sentence the objecting State either writes or does not write.
The ordinary objection leaves the treaty standing between the two States, and its consequence is the one Article 21(3) sets out. The Netherlands wrote the second kind when it responded to the reservations filed against Article IX of the Convention on the Prevention and Punishment of the Crime of Genocide, 1948, declaring that it does not deem any State which has made or which will make such a reservation to be a party to the Convention. It named twelve States, India among them.
On the Netherlands’ position there is accordingly no treaty relationship with those States under the Convention at all, rather than a modified one. The United Kingdom has taken the narrower course, stating consistently that it is unable to accept reservations in respect of Article IX, without going on to deny that the reserving States are parties.
Legal effects of reservations to treaties under Article 21
Once a State has accepted a reservation, Article 21 settles what the treaty between the two of them now contains, and the answer is that it has changed for both of them and for nobody else. A reservation established in accordance with Articles 19, 20 and 23 modifies the provisions to which it relates, to the extent of the reservation, as between the reserving State and that one other party.
Article 21(2) states the limit on that. The reservation does not modify the provisions of the treaty for the other parties inter se. A multilateral convention carrying fifteen reservations stays one instrument among the States that reserved nothing, with a separate bilateral variation between each reserving State and each State that accepted its reservation.
Reciprocity of reservations under Article 21(1)
A reservation operates in both directions. Article 21(1)(a) modifies the reserved provisions for the reserving State in its relations with the accepting party, and Article 21(1)(b) modifies those same provisions to the same extent for that accepting party in its relations with the reserving State. The reserving State loses the benefit of the provision along with the burden of it.
Take a convention obliging each party to extradite or prosecute a person found on its territory, and a State that reserves that obligation so far as its own nationals are concerned. Against a party that accepted the reservation, the reserving State need not surrender its own nationals. That same party is equally released from the obligation to surrender its nationals to the reserving State, because Article 21(1)(b) hands it the reservation as well.
Article 21(3) produces a different result for a State that objected without opposing the entry into force of the treaty between itself and the reserving State. As between those two, the provisions to which the reservation relates do not apply at all, to the extent of the reservation. The provision is not modified for them, it is absent.
The distance between those two outcomes is narrower than it looks, and on some reservations it comes to nothing. Where the reservation simply excludes a provision, acceptance and a simple objection leave the two States in much the same place. Where the reservation modifies a provision instead of excluding it, the two routes part company, because acceptance gives both States the modified provision while a simple objection leaves them with no provision on that point at all. A treaty in force still binds the parties and must be performed by them in good faith, which is the rule pacta sunt servanda states, and a reservation changes the content of that obligation without touching the duty to keep it.
The status of invalid reservations
Articles 19 to 23 do not say what happens when a reservation fails the Article 19 test. Article 21 gives effects only to a reservation established in accordance with Articles 19, 20 and 23, and the Convention says nothing further. Three answers have been offered since, and they do not agree.
The Human Rights Committee gave the first in General Comment No. 24 of 4 November 1994. The Committee claimed the power to determine the compatibility of a reservation to the International Covenant on Civil and Political Rights, and said that the normal consequence of an unacceptable reservation is that the reservation is severable, so that the Covenant remains operative for the reserving party without the benefit of it. France, the United Kingdom and the United States rejected both propositions. France took the position that severability is incompatible with the existing law of treaties, and that the consequence of an invalid reservation is that the State’s consent is invalid and the State is not a party.
The International Law Commission took a middle course in its Guide to Practice on Reservations to Treaties, adopted on 11 August 2011. Guideline 4.5.3 makes the status of the author of an invalid reservation turn on that State’s own intention. The presumption is that the State is a contracting State without the benefit of the reservation, and it may state at any time that it does not intend to be bound on those terms.
An invalid reservation had already produced the Commission’s result on facts, long before the Commission wrote the presumption down. Switzerland had entered what it called an interpretative declaration to Article 6(1) of the European Convention on Human Rights, and in Belilos v. Switzerland, decided on 29 April 1988, the European Court of Human Rights read that statement on its substance rather than on its label. The Court held that it did not satisfy two of the requirements of the then Article 64 of the Convention and must therefore be held invalid, and it decided the case on the footing that Switzerland was bound by the Convention irrespective of the validity of the declaration.
Written form and withdrawal of reservations under Articles 22 and 23
A reservation, an acceptance, an objection and a withdrawal are effective only in writing, and only once the right State has received notice of them. Article 23(1) requires a reservation, an express acceptance of a reservation and an objection to a reservation to be formulated in writing and communicated to the contracting States and to the other States entitled to become parties to the treaty. Article 23(4) applies the same requirement to a withdrawal.
Article 23(2) carries the requirement most often missed. A reservation formulated when signing a treaty that is subject to ratification, acceptance or approval must be formally confirmed by the reserving State when it expresses its consent to be bound, and it is then considered as having been made on the date of its confirmation. A reservation announced at signature and never confirmed at ratification has no effect. Article 23(3) removes the corresponding trap on the other side, by providing that an express acceptance of, or an objection to, a reservation made before its confirmation does not itself require confirmation.
Withdrawal runs on fewer conditions than any other step in the scheme. A reservation may be withdrawn at any time under Article 22(1), and the consent of a State which has accepted it is not required, unless the treaty provides otherwise. An objection may equally be withdrawn at any time under Article 22(2).
A State that accepted a reservation gained a reciprocal benefit under Article 21(1)(b), and the reserving State can end that benefit by withdrawing the reservation without asking anyone. Article 22(3) fixes when the withdrawal takes effect. The withdrawal of a reservation becomes operative in relation to another contracting State only when notice of it has been received by that State, and the withdrawal of an objection only when notice has been received by the State which formulated the reservation, so the date of despatch counts for nothing.
Reservations to treaties in Indian practice
India applies Articles 19 to 23 as customary international law rather than as obligations owed under the Vienna Convention, because India is not a party to that Convention. The Vienna Convention on the Law of Treaties entered into force on 27 January 1980 and has 119 parties and 45 signatories, and India appears on neither list.
That absence changes little in the mechanics. India’s own instruments follow the same steps the Convention prescribes, with reservations formulated at ratification, communicated to the depositary in writing, and answered by other States through objections filed with the same depositary. The instruments themselves are settled by the Union executive, which holds the treaty-making power under the Constitution of India.
India’s reservation to Article IX of the Genocide Convention
India ratified the Convention on the Prevention and Punishment of the Crime of Genocide on 27 August 1959 with a reservation to Article IX. The reservation declares that for the submission of any dispute in terms of that article to the jurisdiction of the International Court of Justice, the consent of all the parties to the dispute is required in each case.
The Netherlands objected, in the second of the two forms Article 20(4)(b) allows. Its declaration states that it does not deem any State which has made or which will make such a reservation to be a party to the Convention, and it lists India among twelve States. The United Kingdom has stated consistently that it is unable to accept reservations in respect of Article IX, without denying that the reserving States are parties.
What India’s reservation does is what Rwanda’s reservation did in 2006. A State bringing a Genocide Convention claim against India before the International Court of Justice would meet the same jurisdictional answer the Democratic Republic of the Congo received, unless India consented to that particular dispute going to the Court.
Declarations that operate as reservations in India’s treaty practice
The words “however phrased or named” in Article 2(1)(d) reach further into Indian practice than the reservations India has labelled as such. India ratified the Convention on the Elimination of All Forms of Discrimination against Women on 9 July 1993 with two declarations and one reservation.
The reservation is to Article 29(1), the dispute settlement clause, and states that India does not consider itself bound by it. The two declarations go to substance instead. On Articles 5(a) and 16(1), India declared that it would abide by and ensure those provisions in conformity with its policy of non-interference in the personal affairs of any community without that community’s initiative and consent. On Article 16(2), which requires compulsory registration of marriages, India declared that it supports the principle but that registration is not practical in a country of India’s size and variety of customs, religions and levels of literacy.
Whether a statement qualifying how a substantive obligation applies is a declaration or a reservation is decided on its substance, which is what the European Court of Human Rights settled in Belilos. India’s declarations have not been tested before any court, and the influence CEDAW has had in India since ratification has come through Indian courts.
The same line runs through India’s law of the sea practice. India ratified the United Nations Convention on the Law of the Sea on 29 June 1995, and that Convention bars reservations by Article 309 while permitting declarations by Article 310, provided a declaration does not purport to exclude or to modify the legal effect of the Convention’s provisions in their application to the declaring State. India’s declaration states that the provisions of the Convention do not authorise other States to carry out military exercises or manoeuvres in the exclusive economic zone or on the continental shelf without the consent of the coastal State, in particular those involving the use of weapons or explosives.
Bangladesh, Brazil, Malaysia, Pakistan and Uruguay made declarations to similar effect. The United States is not a party to the Convention and does not accept the consent requirement, and in April 2021 it sailed a destroyer through India’s exclusive economic zone near the Lakshadweep Islands without requesting India’s consent. Whether a declaration of that kind stays on the permitted side of Article 310 is the question Article 2(1)(d) poses about every such statement, and the law of the sea has carried it unresolved since.
Frequently asked questions
Is a reservation to a treaty the same thing as an interpretative declaration?
They are different in principle and often the same thing in substance. A reservation purports to exclude or modify the legal effect of a provision for the reserving State, while an interpretative declaration only states how that State reads a provision it accepts in full. Article 2(1)(d) applies the definition “however phrased or named”, so the label a State chooses does not decide the question, and in Belilos v. Switzerland the European Court of Human Rights treated a declaration as a reservation and then held it invalid.
Can a State make a reservation after it has already ratified a treaty?
A State cannot, because Article 19 permits a reservation only when a State signs, ratifies, accepts, approves or accedes to a treaty, so the opportunity closes at the moment consent to be bound is expressed. A State that formulated a reservation at signature must still confirm it formally at ratification under Article 23(2), and a reservation never confirmed at that point has no effect.
What happens to the treaty when another State objects to a reservation?
That depends on what the objecting State wrote. An ordinary objection under Article 20(4)(b) leaves the treaty in force between the two States, and under Article 21(3) the provisions to which the reservation relates then do not apply between them to the extent of the reservation. Where the objecting State definitely expresses a contrary intention, the treaty does not come into force between the two of them at all.
Is India bound by the Vienna Convention on the Law of Treaties?
India is not a party to the Vienna Convention, which has 119 parties and 45 signatories and lists India among neither. The rules on reservations still govern Indian treaty practice as customary international law, and India’s instruments are drafted and communicated in the form Articles 19 to 23 prescribe.
Can a reservation be withdrawn after another State has accepted it?
Yes, and the accepting State cannot stop it. Article 22(1) permits withdrawal at any time unless the treaty provides otherwise, and it expressly dispenses with the consent of a State which has accepted the reservation. The withdrawal becomes operative in relation to that State only when notice of it has been received under Article 22(3), and it takes back the reciprocal benefit the accepting State had under Article 21(1)(b).
References
- Vienna Convention on the Law of Treaties, concluded at Vienna on 23 May 1969, articles cited being 2(1)(d), 19, 20, 21, 22 and 23. https://legal.un.org/ilc/texts/instruments/english/conventions/1_1_1969.pdf
- Vienna Convention on the Law of Treaties, depositary status showing entry into force on 27 January 1980, 119 parties and 45 signatories, with India recorded as neither. https://treaties.un.org/Pages/ViewDetailsIII.aspx?src=TREATY&mtdsg_no=XXIII-1&chapter=23&Temp=mtdsg3&clang=_en
- Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide, Advisory Opinion of 28 May 1951, International Court of Justice. https://www.icj-cij.org/case/12
- Armed Activities on the Territory of the Congo (New Application: 2002) (Democratic Republic of the Congo v. Rwanda), judgment on jurisdiction and admissibility of 3 February 2006, International Court of Justice. https://www.icj-cij.org/case/126
- Belilos v. Switzerland, application number 10328/83, judgment of 29 April 1988, European Court of Human Rights. https://hudoc.echr.coe.int/eng?i=001-57434
- Human Rights Committee, General Comment No. 24, CCPR/C/21/Rev.1/Add.6, 4 November 1994, on reservations made upon ratification or accession to the Covenant. https://hrlibrary.umn.edu/gencomm/hrcom24.htm
- International Law Commission, Guide to Practice on Reservations to Treaties, adopted 11 August 2011, guideline cited being 4.5.3. https://legal.un.org/ilc/texts/instruments/english/draft_articles/1_8_2011.pdf
- United Nations Convention on the Law of the Sea, 1982, articles cited being 309 and 310. https://www.un.org/depts/los/convention_agreements/texts/unclos/part17.htm
- Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction, articles cited being 10 and 70, with the depositary record of declarations and exceptions. https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXI-10&chapter=21&clang=_en
- BBNJ Agreement, entry into force on 17 January 2026. https://news.un.org/en/story/2026/01/1166762
- WHO Pandemic Agreement, resolution WHA78.1 of 20 May 2025, articles cited being 12, 25, 26 and 33. https://apps.who.int/gb/ebwha/pdf_files/WHA78/A78_R1-en.pdf
- Convention on the Prevention and Punishment of the Crime of Genocide, 1948, depositary record of India’s ratification of 27 August 1959, its reservation to article IX, and the objections of the Netherlands and the United Kingdom. https://treaties.un.org/Pages/ViewDetails.aspx?src=TREATY&mtdsg_no=IV-1&chapter=4&clang=_en
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Convention on the Elimination of All Forms of Discrimination against Women, 1979, depositary record of India’s ratification of 9 July 1993, its declarations on articles 5(a), 16(1) and 16(2), and its reservation to article 29(1). https://treaties.un.org/Pages/ViewDetails.aspx?src=TREATY&mtdsg_no=IV-8&chapter=4&clang=_en
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Summary of the judgment of 3 February 2006 in Armed Activities on the Territory of the Congo, recording that Rwanda’s reservation bears on the jurisdiction of the Court and does not affect substantive obligations relating to acts of genocide themselves. https://www.icj-cij.org/node/103925
- Observer Research Foundation, on the maritime claims the United States challenges in India’s exclusive economic zone. https://www.orfonline.org/research/what-excessive-maritime-claims-is-the-us-challenging-india-over
- Deccan Herald, report of the United States freedom of navigation operation near the Lakshadweep Islands in April 2021. https://www.deccanherald.com/world/us-warship-challenges-indias-excessive-maritime-claims-near-lakshadweep-islands-972304.html
This article is for informational and educational purposes only and does not constitute legal advice. Readers should consult a qualified advocate before acting on any point discussed here.