Law of Treaties

The Law of Treaties is the branch of International Law that governs the making, interpretation, application, modification, suspension and termination of treaties between States. Treaties are one of the principal sources of international obligations and play a central role in regulating relations between States.

The principal codification of the law of treaties is the Vienna Convention on the Law of Treaties, 1969 (VCLT).

Meaning of a Treaty

Under Article 2(1)(a) of the Vienna Convention on the Law of Treaties, 1969, a treaty is an international agreement concluded between States in written form and governed by International Law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation.

Therefore, an international agreement may be called:

• treaty;
• convention;
• agreement;
• protocol;
• covenant;
• charter;
• statute;
• exchange of notes.

The name does not determine whether it is legally a treaty.

Essential Elements of a Treaty

A treaty generally involves:

1. International agreement
2. States as parties, for the purposes of the VCLT
3. Written form
4. Governance by International Law
5. Intention to create legal obligations

Thus:

Agreement between States

↓

Intended to create international legal obligations

↓

Governed by International Law

↓

Treaty

Vienna Convention on the Law of Treaties, 1969

The Vienna Convention on the Law of Treaties, 1969 is the principal international instrument codifying the law relating to treaties.

It deals with:

• conclusion of treaties;
• consent to be bound;
• reservations;
• entry into force;
• observance;
• interpretation;
• amendment;
• invalidity;
• termination;
• suspension.

The Convention applies primarily to treaties between States.

Pacta Sunt Servanda

One of the most fundamental principles of treaty law is pacta sunt servanda.

Article 26 VCLT provides that every treaty in force is binding upon the parties and must be performed by them in good faith.

The principle can be expressed as:

Treaty in force

↓

Binding on parties

↓

Must be performed in good faith

This is the foundation of the binding force of treaties.

Good Faith

Good faith is central to treaty law.

States must not:

• deliberately defeat treaty obligations;
• manipulate treaty provisions dishonestly;
• invoke treaty obligations selectively in bad faith.

Good faith applies both to the performance and interpretation of treaties.

Domestic Law and Treaty Obligations

Article 27 VCLT establishes that a State generally may not invoke its internal law as justification for its failure to perform a treaty.

Therefore:

International treaty obligation

↓

Domestic law conflicts

↓

State cannot ordinarily rely on domestic law to escape its international obligation

There is an important qualification concerning Article 46 VCLT, dealing with internal law concerning competence to conclude treaties.

Capacity to Conclude Treaties

Under Article 6 VCLT, every State possesses capacity to conclude treaties.

The State acts through persons authorised under International Law or domestic constitutional arrangements.

Representatives of States

Certain persons are recognised as having authority to represent a State for particular treaty purposes.

Under Article 7 VCLT, this includes:

• Heads of State;
• Heads of Government;
• Ministers for Foreign Affairs.

They generally do not need to produce full powers for acts connected with treaty conclusion.

Other representatives may require full powers.

Full Powers

Full powers are formal authority granted by a State authorising a person to represent it for specified treaty acts.

For example:

State → gives full powers

↓

Representative → negotiates/signs treaty

↓

State → becomes bound according to applicable procedure

Negotiation of Treaties

Treaties generally begin through negotiation between States.

The negotiating States discuss:

• rights;
• obligations;
• definitions;
• procedures;
• implementation mechanisms.

Once agreement is reached, the treaty text is generally adopted.

Adoption of the Text

Article 9 VCLT deals with adoption of treaty texts.

The adoption of the text is distinct from the later question of whether a State has consented to be bound.

This distinction is important:

Adoption of text ≠ Consent to be bound

Authentication of the Text

After adoption, the treaty text may be authenticated.

Authentication establishes that the text is the agreed and authoritative version.

Methods may include:

• signature;
• initialling;
• procedure agreed by negotiating States.

Consent to Be Bound

A State can express consent to be bound through several methods recognised by the VCLT, including:

• signature;
• exchange of instruments;
• ratification;
• acceptance;
• approval;
• accession.

The method depends upon the treaty and the intention of the States.

Signature

Signature can have different legal effects.

In some treaties, signature itself expresses consent to be bound.

In others, signature merely authenticates the text and indicates that further action, such as ratification, is required.

Therefore:

Signature does not always mean that the State is already fully bound by the treaty.

Ratification

Ratification is the formal international act by which a State confirms its consent to be bound by a treaty where the treaty requires or permits ratification.

It is distinct from domestic approval procedures.

A simplified process is:

Negotiation

↓

Signature

↓

Ratification

↓

Consent to be bound

↓

Entry into force

Acceptance and Approval

Acceptance and approval are alternative methods of expressing consent to be bound.

Their legal effect under the VCLT is generally comparable to ratification.

Accession

Accession occurs when a State becomes a party to a treaty that it did not sign during the period when the treaty was open for signature.

Thus:

Treaty already concluded

↓

State did not sign

↓

State later joins

↓

Accession

Entry into Force

A treaty becomes legally operative according to the conditions established in the treaty or otherwise agreed by the parties.

The treaty may specify:

• a particular date;
• number of ratifications;
• other conditions.

Reservations

A reservation is a unilateral statement made by a State when signing, ratifying, accepting, approving or acceding to a treaty, whereby it purports to exclude or modify the legal effect of certain provisions of the treaty in their application to that State.

Reservations are governed principally by Articles 19–23 VCLT.

Permissibility of Reservations

Under Article 19, a State may formulate a reservation unless:

1. the treaty prohibits reservations;
2. the treaty permits only specified reservations and the proposed reservation is not among them; or
3. the reservation is incompatible with the object and purpose of the treaty.

Objection to a Reservation

Another State may object to a reservation.

The legal consequences depend upon whether the objecting State:

• accepts the reserving State as a treaty party; or
• intends to prevent treaty relations from arising between itself and the reserving State.

Interpretation of Treaties

Treaty interpretation is primarily governed by Articles 31–33 VCLT.

Article 31 — General Rule

A treaty must be interpreted:

• in good faith;
• according to the ordinary meaning of the terms;
• in their context;
• in light of the treaty’s object and purpose.

This is the central rule of treaty interpretation.

Article 32 — Supplementary Means

Supplementary means of interpretation may be used, including:

• preparatory work of the treaty (travaux préparatoires);
• circumstances of its conclusion.

They may be used particularly to:

• confirm the meaning reached under Article 31; or
• determine meaning where Article 31 leaves the meaning ambiguous or obscure;
• resolve an interpretation leading to a manifestly absurd or unreasonable result.

Article 33 — Treaties Authenticated in Multiple Languages

Where a treaty is authenticated in two or more languages, each authentic text generally has equal authority unless the treaty provides otherwise.

Where differences arise, Article 33 provides rules for determining the appropriate interpretation.

Amendment of Treaties

Treaties may be amended by agreement between the parties.

The VCLT distinguishes between:

• amendment of treaties generally;
• modification of multilateral treaties between certain parties.

The precise procedure depends upon the treaty and the VCLT provisions.

Invalidity of Treaties

A treaty may be invalid in certain circumstances.

Important grounds include:

• error;
• fraud;
• corruption of a representative;
• coercion of a representative;
• coercion of a State by threat or use of force;
• conflict with jus cogens.

Error

Under Article 48 VCLT, a State may invoke an error in certain circumstances where the error relates to a fact or situation assumed to exist when the treaty was concluded and formed an essential basis of its consent.

Not every mistake is sufficient.

Fraud

Under Article 49 VCLT, fraud by another negotiating State may entitle a State to invoke the fraud as invalidating its consent to be bound.

Corruption of a Representative

Article 50 VCLT deals with corruption of a State’s representative.

Where the State’s consent was procured through corruption by another negotiating State, the State may invoke this as a ground affecting its consent.

Coercion of a Representative

Under Article 51, the expression of a State’s consent is without legal effect if it has been procured through coercion of its representative by acts or threats directed against them.

Coercion of a State

Article 52 VCLT provides that a treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of International Law embodied in the Charter of the United Nations.

Jus Cogens

A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general International Law (jus cogens).

This is provided by Article 53 VCLT.

Examples of norms widely regarded as having jus cogens status include the prohibitions of:

• genocide;
• slavery;
• torture;
• aggression, subject to the precise scope of the norm.

Supervening Jus Cogens

Article 64 VCLT deals with the emergence of a new peremptory norm.

If a new jus cogens norm emerges, an existing treaty that conflicts with it becomes void and terminates.

Termination of Treaties

A treaty may terminate:

• according to its provisions;
• by consent of the parties;
• in accordance with the VCLT;
• in certain circumstances recognised by International Law.

Withdrawal

A State may withdraw from a treaty where:

• the treaty permits withdrawal; or
• withdrawal is otherwise allowed under the applicable legal framework.

Where the treaty is silent, Article 56 VCLT establishes a restrictive approach to unilateral withdrawal.

Material Breach

Article 60 VCLT deals with termination or suspension because of material breach.

A material breach involves:

• repudiation of the treaty not sanctioned by the Convention; or
• violation of a provision essential to the accomplishment of the treaty’s object or purpose.

The consequences differ between:

• bilateral treaties;
• multilateral treaties.

Impossibility of Performance

Under Article 61 VCLT, a party may invoke the impossibility of performing a treaty as a ground for terminating or withdrawing from it where the impossibility results from the permanent disappearance or destruction of an object indispensable for the execution of the treaty.

Temporary impossibility may justify suspension rather than termination.

Fundamental Change of Circumstances

Article 62 VCLT recognises fundamental change of circumstances as a limited ground for terminating or withdrawing from a treaty.

The doctrine is subject to strict conditions.

The change must:

• have been unforeseen;
• constitute an essential basis of the parties’ consent;
• radically transform the extent of obligations still to be performed.

It cannot generally be invoked for treaties establishing boundaries.

Rebus Sic Stantibus

The principle of rebus sic stantibus is associated with Article 62.

It means, broadly:

“Things standing thus.”

It reflects the idea that a fundamental and unforeseen change in circumstances may, in exceptional situations, affect continuing treaty obligations.

It is interpreted narrowly because unrestricted reliance upon it would undermine treaty stability.

Severance of Treaty Provisions

In certain circumstances, invalidity or termination may affect only particular provisions rather than the entire treaty.

The VCLT establishes rules concerning when provisions may be separated from the remainder of the treaty.

Effects of Termination

When a treaty terminates, the parties are generally released from the obligation to perform it for the future.

However, termination does not necessarily erase:

• rights;
• obligations;
• legal situations

that were created through performance before termination, subject to the applicable treaty and VCLT rules.

Treaties and Third States

The general principle is:

A treaty does not create obligations or rights for a third State without its consent.

This principle is reflected in Articles 34–38 VCLT.

Article 34

A treaty does not create obligations or rights for a third State without its consent.

Article 35

An obligation may arise for a third State if the parties intend to create the obligation and the third State expressly accepts it in writing.

Article 36

A right may arise for a third State if the parties intend to grant it and the third State assents, with assent generally presumed unless otherwise indicated.

Treaties and International Organisations

The VCLT 1969 primarily concerns treaties between States.

A separate Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations, 1986 addresses treaties involving international organisations.

Treaty Registration

Article 102 of the UN Charter requires treaties and international agreements entered into by UN Members to be registered with and published by the UN Secretariat.

An important consequence is that a party cannot invoke an unregistered treaty or international agreement before an organ of the United Nations.

Treaty Interpretation and International Courts

International courts frequently interpret treaty provisions according to the rules reflected in Articles 31 and 32 VCLT.

Even where the VCLT is not directly applicable, these interpretation principles have had significant influence on general treaty practice.

Important Cases

Reservations to the Genocide Convention, 1951

The ICJ’s Advisory Opinion on Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide (1951) is a landmark authority on treaty reservations.

The Court emphasised compatibility of reservations with the object and purpose of the treaty.

North Sea Continental Shelf, 1969

The ICJ considered treaty provisions, customary International Law and the relationship between treaty obligations and customary rules.

Gabcíkovo-Nagymaros Project, 1997

The ICJ considered:

• fundamental change of circumstances;
• impossibility of performance;
• necessity;
• treaty obligations.

The case is important for the limited circumstances in which States may avoid treaty obligations.

Qatar v. Bahrain, 1994

The ICJ considered whether certain written instruments constituted international agreements and therefore created binding obligations.

The case demonstrates that the substance and intention of an instrument, rather than merely its title, are important.

Treaty Law and Customary International Law

Treaties and customary International Law are separate sources of international obligations but may interact.

A treaty provision may:

• codify an existing customary rule;
• crystallise an emerging customary rule;
• contribute to the development of customary International Law.

However, a treaty does not automatically bind non-parties merely because it exists.

Treaty vs Convention

In International Law, the terms treaty and convention are often used interchangeably as forms of international agreement.

The legal effect depends upon:

• the instrument;
• the intention of the parties;
• applicable International Law.

Treaty vs Memorandum of Understanding

Not every international instrument labelled an MOU is legally binding.

The key question is whether the parties intended to create legal obligations governed by International Law.

Therefore:

Name of document ≠ decisive

Intention + legal character = important

Treaty vs Executive Agreement

Different States use different constitutional procedures for international agreements.

Whether an agreement is legally binding internationally depends upon the applicable International Law and the State’s constitutional arrangements.

Domestic classification does not necessarily determine the international legal character of the agreement.

Fundamental Principles

The Law of Treaties rests on several fundamental principles:

1. Pacta Sunt Servanda

Treaties in force are binding and must be performed in good faith.

2. Good Faith

States must perform and interpret treaties honestly and consistently with their obligations.

3. Consent

Treaty obligations generally arise from the consent of States.

4. Sovereign Equality

States participate in treaty-making as sovereign and legally equal entities.

5. Stability of Treaties

Treaty obligations should not be easily disregarded or terminated.

6. Respect for Jus Cogens

Treaties cannot validly override peremptory norms of general International Law.

Treaty-Making Process

A simplified treaty-making process is:

Negotiation

↓

Adoption of text

↓

Authentication

↓

Signature

↓

Ratification / Acceptance / Approval

↓

Exchange or deposit of instruments

↓

Entry into force

↓

Performance

↓

Interpretation / Amendment

↓

Possible Termination

Topic at a Glance

Topic	Key Rule
Principal instrument	Vienna Convention on the Law of Treaties, 1969
Treaty	International agreement governed by International Law
Article 6	Capacity of States
Article 7	Representatives/full powers
Article 9	Adoption of text
Articles 11–17	Consent to be bound
Articles 19–23	Reservations
Article 24	Entry into force
Article 26	Pacta sunt servanda
Article 27	Internal law cannot generally justify non-performance
Articles 31–33	Interpretation
Articles 34–38	Third States
Articles 39–41	Amendment/modification
Articles 46–53	Invalidity
Article 52	Coercion by threat/use of force
Article 53	Jus cogens
Article 54	Termination/withdrawal
Article 56	Withdrawal where treaty silent
Article 60	Material breach
Article 61	Impossibility of performance
Article 62	Fundamental change of circumstances
Article 64	New jus cogens norm
Article 102 UN Charter	Registration of treaties

Quick Revision

• Law of Treaties governs the conclusion, operation, interpretation, amendment and termination of treaties.
• The principal codification is the Vienna Convention on the Law of Treaties, 1969.
• Article 2(1)(a) → definition of treaty.
• Article 6 → capacity of States.
• Article 7 → representatives and full powers.
• Article 9 → adoption of treaty text.
• Articles 11–17 → methods of expressing consent to be bound.
• Articles 19–23 → reservations.
• Article 24 → entry into force.
• Article 26 → pacta sunt servanda.
• Article 27 → domestic law generally cannot justify failure to perform a treaty.
• Articles 31–33 → treaty interpretation.
• Articles 34–38 → third States.
• Article 52 → coercion of a State by threat or use of force.
• Article 53 → conflict with jus cogens.
• Article 60 → material breach.
• Article 61 → impossibility of performance.
• Article 62 → fundamental change of circumstances.
• Article 64 → emergence of new jus cogens.
• Article 102 UN Charter → registration and publication of treaties.
• Important cases:
  • Reservations to the Genocide Convention (1951)
  • North Sea Continental Shelf (1969)
  • Gabcíkovo-Nagymaros Project (1997)
  • Qatar v. Bahrain (1994)

Conclusion

The Law of Treaties provides the legal framework governing the creation, performance, interpretation, modification and termination of international agreements. The Vienna Convention on the Law of Treaties, 1969 is the principal instrument codifying these rules. Treaty law is founded on State consent, good faith and pacta sunt servanda, under which treaties in force are binding and must be performed in good faith. The Convention establishes detailed rules concerning treaty-making, representatives, adoption and authentication of texts, ratification, accession, reservations and entry into force. It also provides the principal rules of treaty interpretation in Articles 31–33, requiring interpretation in good faith according to ordinary meaning, context and object and purpose. The Convention further regulates invalidity, termination, material breach, impossibility of performance and fundamental change of circumstances. Particularly important are the rules concerning coercion and jus cogens, which ensure that treaty obligations cannot be validly created through prohibited force or used to override peremptory norms of general International Law. Treaties also generally cannot impose obligations on third States without their consent. Through these principles, the Law of Treaties provides stability and predictability in international relations while recognising the sovereign consent of States and the supremacy of fundamental rules of International Law.