Treaties in International Law

Treaties in International Law

Treaties are among the most important sources of international law. They allow states to create legally binding obligations through formal agreement and provide a structured framework for international cooperation.

A treaty can regulate almost any subject capable of being addressed through international agreement. States use treaties to establish diplomatic relations, settle borders, protect human rights, regulate international trade, cooperate against crime, protect the environment, govern the use of oceans and other international spaces, establish international organizations, and address armed conflict.

Unlike a domestic statute, a treaty is not normally enacted by a single national legislature acting for an entire population. It is an international agreement concluded by subjects of international law and governed by international law.

The law governing treaties is itself a major branch of international law. One of its principal instruments is the Vienna Convention on the Law of Treaties of 1969, which establishes rules concerning the formation, interpretation, application, amendment, and termination of treaties.

For a broader introduction to the subject, the Cornell Law School Legal Information Institute’s Wex materials on international law provide useful background on treaties as part of the international legal system.

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What Is a Treaty?

A treaty is an international agreement governed by international law.

The term “treaty” is used in a broad legal sense. International agreements can have different names, including:

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

The name alone does not determine whether an instrument is legally a treaty.

What matters is the legal character and intention of the agreement.

For example, two states might sign a document called a “declaration” that is merely political and non-binding. Conversely, an instrument with another title may establish binding international obligations.

The central question is whether the parties intended to create an agreement governed by international law.

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Treaties as a Source of International Law

Treaties are one of the principal sources of international law.

They have particular importance because they allow states to establish clearly defined obligations.

A treaty may specify:

• what each party must do;
• what each party must not do;
• when obligations begin;
• how compliance will be monitored;
• how disputes will be resolved;
• how the treaty may be amended;
• whether reservations are permitted;
• how the treaty may be terminated; and
• which institutions are responsible for implementing it.

Treaties therefore provide a degree of precision that may be more difficult to achieve through customary international law.

At the same time, treaties do not exist outside the broader international legal system. Their formation and operation are governed by international law, including the rules concerning treaty interpretation and state responsibility.

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The Vienna Convention on the Law of Treaties

The Vienna Convention on the Law of Treaties (VCLT) is the central international instrument concerning the law of treaties.

It was adopted in 1969 and entered into force in 1980.

The Convention addresses many fundamental questions, including:

• how treaties are concluded;
• how states express consent to be bound;
• reservations;
• entry into force;
• provisional application;
• interpretation;
• amendment;
• invalidity;
• termination;
• suspension; and
• withdrawal.

The Convention is sometimes described as the “treaty on treaties.”

That description is useful because it captures its central function: it establishes rules governing how international agreements operate as legal instruments.

Not every state is a party to the Vienna Convention. Nevertheless, many of its provisions reflect customary international law and are therefore important beyond the Convention’s formal membership.

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Who Can Conclude Treaties?

States are the traditional and most important treaty-making subjects.

A sovereign state generally possesses the capacity to conclude treaties.

International organizations can also conclude international agreements where they possess the necessary legal capacity.

The treaty-making capacity of an international organization depends upon its constituent instruments and the applicable rules of international law.

Individuals and private companies ordinarily do not possess treaty-making capacity in the same sense as states.

A contract between two corporations located in different countries is therefore not normally a treaty merely because it has an international dimension.

It is a private agreement governed by the applicable domestic or international private law framework.

This distinction is fundamental:

An international contract is not automatically an international treaty.

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Treaty Negotiation

Treaties usually begin with negotiation.

States may negotiate directly through diplomatic representatives or through an international organization or diplomatic conference.

Negotiations can involve extensive discussion concerning:

• the scope of the agreement;
• definitions;
• rights and obligations;
• exceptions;
• enforcement mechanisms;
• dispute resolution;
• institutional structures;
• financial responsibilities;
• implementation periods; and
• amendment procedures.

Complex multilateral treaties can take years to negotiate.

The negotiating states may have radically different interests. The final text therefore frequently represents a compromise among competing political, economic, security, and legal considerations.

International treaty negotiation is consequently both a legal and diplomatic process.

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Adoption of the Treaty Text

After negotiations produce an agreed text, the participants formally adopt the treaty text.

Adoption means that the negotiating parties have established the text that will constitute the proposed agreement.

Adoption does not necessarily mean that every state has already become legally bound by the treaty.

This distinction is important.

A state can participate in negotiating and adopting a treaty without ultimately becoming a party to it.

The state must normally take a further step to express its consent to be legally bound.

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Signature

Signature is one possible method by which a state expresses its consent to be bound by a treaty.

However, signature does not always have the same legal effect.

Some treaties provide that signature itself constitutes consent to be bound.

In other cases, signature is followed by ratification, approval, or acceptance.

A treaty may therefore be signed by a state without immediately becoming fully binding upon that state.

Signature can also create more limited obligations. Under the Vienna Convention, a state that has signed a treaty is generally expected to refrain from acts that would defeat the treaty’s object and purpose before it has made clear that it does not intend to become a party.

The precise legal consequences therefore depend upon the treaty and the circumstances.

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Ratification

Ratification is a formal process through which a state confirms its consent to be bound by a treaty.

The constitutional procedure for ratification differs from country to country.

In some states, the executive branch has substantial authority over treaty-making. In others, legislative approval is required for particular categories of treaties.

The international act of ratification should therefore be distinguished from the domestic constitutional process that may precede it.

This distinction can be especially important in constitutional law.

A country’s constitution may establish internal procedures that government officials must follow before the state can validly express consent internationally.

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Accession

A state that did not participate in negotiating or signing a treaty may sometimes become a party through accession.

Accession allows a state to express its consent to be bound after the treaty has already been adopted or entered into force.

Whether accession is available depends upon the treaty.

Some treaties are open to accession by additional states. Others limit participation to specified states or categories of states.

Accession is therefore another mechanism through which a state can become a treaty party without having been an original signatory.

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Entry Into Force

A treaty becomes legally operative according to its entry-into-force provisions.

The treaty itself normally specifies the conditions that must be satisfied.

For example, a multilateral treaty may provide that it enters into force after a specified number of states have deposited instruments of ratification or accession.

A bilateral treaty may enter into force after both parties have completed the required procedures.

The distinction between signing a treaty and its entry into force is therefore important.

A treaty can be signed but not yet legally operative.

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Reservations to Treaties

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

Reservations are particularly important in multilateral treaties.

They allow states with different legal or political positions to participate in a treaty while declining to accept particular provisions under specified conditions.

However, reservations are not unlimited.

A reservation may be impermissible where:

• the treaty prohibits reservations;
• the treaty permits only specified reservations and the proposed reservation falls outside those categories; or
• the reservation is incompatible with the treaty’s object and purpose.

Reservations can therefore create complicated questions concerning the relationship between the reserving state and other treaty parties.

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Objections to Reservations

Other states may object to a reservation.

An objection can have different legal consequences depending upon the circumstances and the position taken by the objecting state.

One state may object to a reservation while still accepting that the treaty relationship exists.

Another may object in a manner indicating that it does not accept the treaty relationship with the reserving state.

The legal consequences depend upon the applicable treaty rules and the relevant provisions of the Vienna Convention.

Reservations are consequently an area in which seemingly simple treaty participation can produce complex legal relationships among different states.

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Treaty Interpretation

Treaty interpretation is one of the most important areas of international treaty law.

A treaty cannot be applied effectively unless its provisions can be interpreted.

The Vienna Convention places particular emphasis on:

• the ordinary meaning of the treaty’s terms;
• the context in which those terms appear;
• the treaty’s object and purpose; and
• good faith.

Interpretation may also involve supplementary materials where appropriate, particularly when the ordinary interpretive approach leaves the meaning ambiguous or obscure or produces an apparently unreasonable result.

International courts and tribunals frequently devote substantial attention to treaty interpretation.

A single phrase can determine the scope of an international obligation.

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The Ordinary Meaning of Treaty Terms

Treaty interpretation begins with the words of the treaty.

The ordinary meaning of a term is important, but it is not considered in isolation.

A treaty must be interpreted in its context and in light of its object and purpose.

This prevents courts from treating individual words as though they existed independently from the rest of the agreement.

For example, the meaning of a term may depend upon:

• surrounding provisions;
• definitions contained elsewhere in the treaty;
• annexes;
• related instruments;
• subsequent agreements between the parties; or
• established practice concerning the treaty.

Interpretation is therefore a structured legal process rather than simply a dictionary exercise.

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Good Faith in Treaty Law

The principle of good faith is fundamental to treaty law.

States are expected to perform their treaty obligations honestly and consistently with the legal purposes of the agreement.

A state cannot ordinarily avoid a treaty obligation simply because compliance has become politically inconvenient.

This principle is closely connected to the doctrine of pacta sunt servanda.

The Latin expression means, broadly, that agreements must be kept.

Together, these principles express one of the foundations of treaty law: states that voluntarily undertake international legal obligations are expected to honor them.

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Pacta Sunt Servanda

The principle of pacta sunt servanda is expressed in the Vienna Convention in the proposition that every treaty in force is binding upon its parties and must be performed in good faith.

The principle is fundamental because treaties would lose much of their legal value if states could freely disregard them whenever circumstances became inconvenient.

International cooperation depends upon the expectation that commitments will be respected.

At the same time, pacta sunt servanda does not mean that treaties can never be terminated, suspended, amended, or challenged.

International law provides specific rules governing those situations.

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Treaties and Domestic Law

An important issue arises when a state becomes internationally bound by a treaty but must implement the treaty within its domestic legal system.

International law and domestic constitutional law address different questions.

International law may determine whether the state has undertaken a treaty obligation.

Domestic law may determine how that obligation operates internally.

Different constitutional systems approach this relationship differently.

Some treaties may operate directly within domestic law. Others may require implementing legislation.

This distinction is particularly important when a person attempts to rely upon an international treaty in a national court.

The fact that a state is internationally bound does not necessarily answer the separate question of whether an individual can invoke the treaty directly before a particular domestic court.

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Breach of a Treaty

A treaty violation occurs when a state fails to perform an applicable treaty obligation.

A breach can take many forms.

For example, a state may:

• fail to perform a required action;
• engage in conduct expressly prohibited by the treaty;
• fail to provide a required legal protection;
• disregard a procedural obligation; or
• act inconsistently with a binding treaty commitment.

The legal consequences depend upon the treaty and the general rules concerning state responsibility.

A treaty breach can generate international responsibility and may lead to diplomatic negotiations, dispute settlement, arbitration, judicial proceedings, or other consequences.

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Can a State Justify Breaching a Treaty Because Its Domestic Law Says So?

As a general principle, a state cannot simply invoke its domestic law as justification for failing to perform an international treaty obligation.

This principle is essential to the stability of international agreements.

If a state could escape an international obligation merely by changing its domestic legislation, treaty commitments would become highly uncertain.

International law therefore maintains a distinction between:

international responsibility, and

domestic constitutional validity or implementation.

Domestic constitutional difficulties may be highly significant internally, but they do not automatically eliminate an international obligation.

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Amendment of Treaties

Treaties can be amended according to applicable international rules.

The treaty itself may establish an amendment procedure.

A multilateral treaty might require:

• a specified number of parties to approve an amendment;
• a conference of states parties;
• a particular voting threshold; or
• ratification by a specified number of states.

An amendment does not necessarily bind every original treaty party automatically.

The legal effect depends upon the amendment provisions and the applicable treaty law.

This can result in different treaty obligations applying to different groups of states.

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Termination of Treaties

A treaty may cease to operate in accordance with its terms or under applicable rules of international law.

Termination may occur through:

• fulfillment of the treaty’s purpose;
• expiration of a specified period;
• agreement of the parties;
• operation of a termination clause;
• withdrawal where withdrawal is permitted;
• material breach in circumstances recognized by international law; or
• other grounds established under treaty law.

Termination should be distinguished from invalidity.

A treaty may be validly created but later terminated.

An invalid treaty, by contrast, involves a defect affecting its legal validity.

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Withdrawal From a Treaty

Withdrawal means that a state ceases to be a party to a treaty according to applicable international rules.

Whether a state may withdraw depends primarily upon the treaty and the relevant rules of international law.

Some treaties contain explicit withdrawal provisions.

Where a treaty does not contain such a provision, international law may impose significant limitations on unilateral withdrawal.

Withdrawal also generally does not erase legal consequences that arose while the treaty was in force.

A state that withdraws from a treaty does not thereby automatically make its previous conduct lawful.

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Material Breach

A serious violation of a treaty can constitute a material breach.

Under the Vienna Convention, a material breach may have particular consequences for the other parties, including in appropriate circumstances providing grounds for suspending or terminating the treaty.

A material breach generally involves:

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

The doctrine reflects an important balance.

Treaties must be respected, but a state may not necessarily be required to continue performing an agreement when another party has fundamentally repudiated the essential bargain.

The doctrine is nevertheless subject to specific legal conditions and should not be confused with an unrestricted right to terminate a treaty whenever another state commits a minor violation.

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Fundamental Change of Circumstances

International treaty law recognizes a narrow doctrine concerning a fundamental change of circumstances, often referred to by the Latin expression rebus sic stantibus.

Under strict conditions, a fundamental change in circumstances may be invoked as a ground for terminating or withdrawing from a treaty.

The doctrine is deliberately narrow.

If states could escape treaty obligations whenever circumstances changed, international agreements would become unstable.

The change must therefore meet demanding legal requirements, including circumstances that were an essential basis of the parties’ consent and whose transformation fundamentally changes the extent of obligations still to be performed.

The doctrine demonstrates the tension between two principles:

the stability of treaty commitments, and

the reality that international circumstances can change profoundly.

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Invalidity of Treaties

A treaty can also be legally invalid under certain circumstances.

International law recognizes specific grounds of invalidity, including certain situations involving:

• error;
• fraud;
• corruption of a state representative;
• coercion of a representative;
• coercion of a state;
• violation of certain fundamental rules concerning treaty-making authority; and
• conflict with a peremptory norm of general international law.

The rules are deliberately restrictive.

International law places a high value on the stability of treaties, so not every mistake or disagreement is sufficient to invalidate an agreement.

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Treaties and Jus Cogens

Treaties occupy an important position in international law, but they are not unlimited.

A treaty cannot validly override a peremptory norm of general international law (jus cogens).

If a treaty conflicts with an existing peremptory norm, the treaty may be invalid.

If a new peremptory norm subsequently emerges, an existing treaty that conflicts with that norm may become subject to termination under the applicable rules.

This establishes an important hierarchy within international law.

States possess substantial freedom to create treaty obligations, but that freedom is not unlimited.

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Treaties and Customary International Law

Treaties and customary international law often interact.

A treaty may:

• codify an existing customary rule;
• develop a rule that later becomes customary;
• coexist with an independent customary rule; or
• establish a rule applicable only among its parties.

This means that a treaty provision and a customary rule can sometimes address the same subject simultaneously.

The two rules may have similar wording but different legal foundations.

This distinction can become crucial when a dispute involves a state that is not party to the relevant treaty.

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Bilateral and Multilateral Treaties

Treaties can be broadly divided into bilateral and multilateral agreements.

Bilateral treaties

These involve two parties.

They are frequently used for:

• boundary agreements;
• extradition;
• taxation;
• investment;
• trade;
• diplomatic arrangements; and
• mutual legal assistance.

Multilateral treaties

These involve multiple states.

They are particularly common in areas where international cooperation requires common standards.

Examples include treaties concerning:

• human rights;
• environmental protection;
• international humanitarian law;
• international trade;
• international transportation;
• maritime law; and
• international criminal cooperation.

Multilateral treaties can be significantly more complicated because the parties may have different interests, legal systems, and political priorities.

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Treaty Depositaries

Many multilateral treaties designate a depositary.

The depositary performs administrative functions associated with the treaty.

These can include:

• receiving instruments of ratification;
• receiving instruments of accession;
• notifying parties of relevant developments;
• registering the treaty;
• communicating reservations and objections; and
• maintaining official treaty documentation.

The depositary does not ordinarily act as a political authority over the treaty parties.

Its role is primarily administrative and legal.

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Registration and Publication

International treaties may be registered and published through international institutions.

The United Nations Charter contains provisions concerning the registration and publication of treaties and international agreements.

Registration promotes transparency and helps ensure that international agreements are publicly accessible.

It also contributes to the development of an organized international legal record.

The existence of registration requirements should not, however, be confused with the basic validity of every treaty. The legal consequences of failure to register depend upon the applicable legal framework.

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Disputes Concerning Treaties

Treaty disputes can concern almost any aspect of an agreement.

States may disagree about:

• whether a treaty exists;
• whether it entered into force;
• the meaning of a provision;
• whether a reservation is valid;
• whether a state has complied with its obligations;
• whether a breach occurred;
• whether the treaty can be terminated;
• whether withdrawal is permitted; or
• whether another international rule takes precedence.

Disputes may be addressed through:

• negotiation;
• mediation;
• conciliation;
• arbitration;
• international courts; or
• other dispute-resolution mechanisms established by the treaty.

The treaty itself frequently determines the appropriate procedure.

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Why Treaties Matter in International Law

Treaties provide something essential to an international legal system: structured cooperation based upon agreed legal obligations.

Without treaties, states would have considerably less ability to establish detailed and predictable rules governing complex international relationships.

Treaties allow states to transform diplomatic agreements into legal commitments.

They also permit international law to evolve deliberately.

Where customary law develops through state practice over time, treaties can allow states to negotiate a detailed legal framework in advance.

This is especially valuable when dealing with technically complex subjects requiring precise rules.

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Treaties and the Modern International Legal Order

Modern international society could not function in its present form without treaties.

Treaties provide the legal foundation for numerous international institutions and regimes.

They establish organizations, define international boundaries, regulate economic relations, protect individuals, coordinate responses to global problems, and establish mechanisms for international dispute settlement.

At the same time, treaty law demonstrates the fundamental tension at the heart of international law.

States are sovereign and are not generally subject to a universal government.

Yet states voluntarily enter into agreements that restrict their future freedom of action.

The treaty therefore represents a remarkable legal mechanism: sovereign states use their sovereignty to create legally binding limitations upon the future exercise of their sovereignty.

This is one of the central paradoxes—and strengths—of international law.

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Key Takeaways

Treaties are formal international agreements governed by international law and are among the principal sources of international legal obligations.

The most important principles include:

• A treaty is an international agreement governed by international law.
• The name of an instrument does not alone determine whether it is a treaty.
• States are the principal treaty-making subjects, although international organizations may also possess treaty-making capacity.
• Negotiation and adoption of a treaty do not necessarily mean that every participating state is already legally bound.
• Signature, ratification, acceptance, approval, and accession can have different legal effects.
• A treaty becomes operative according to its entry-into-force provisions.
• Reservations allow states, within legal limits, to exclude or modify the effect of particular treaty provisions.
• Treaties must be interpreted according to established principles of international law.
• States are expected to perform treaties in good faith under the principle of pacta sunt servanda.
• Domestic law generally cannot be invoked simply to justify failure to perform an international obligation.
• Treaties can be amended, suspended, terminated, or withdrawn from under specific legal rules.
• A serious violation may constitute a material breach with legally significant consequences.
• Treaties cannot override valid peremptory norms of international law (jus cogens).
• Treaty rules can coexist with, codify, or contribute to the development of customary international law.
• Treaty disputes can be resolved through diplomatic, arbitral, or judicial mechanisms depending upon the applicable legal framework.

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Frequently Asked Questions

What is a treaty in international law?

A treaty is an international agreement governed by international law that creates legal rights and obligations for its parties.

Are all international agreements treaties?

No. Some international agreements are political rather than legally binding. The legal character of an instrument depends upon the applicable law, its terms, and the intention and circumstances surrounding its conclusion.

What is the Vienna Convention on the Law of Treaties?

The Vienna Convention on the Law of Treaties is a major international instrument governing the formation, interpretation, application, amendment, and termination of treaties.

Does signing a treaty make a country legally bound?

Not necessarily. Some treaties make signature sufficient to express consent to be bound, while others require ratification, acceptance, or approval. The treaty’s provisions and applicable international law determine the consequences.

What is treaty ratification?

Ratification is a formal process through which a state confirms its consent to be bound by a treaty. The domestic procedure required before international ratification varies among constitutional systems.

What is a treaty reservation?

A reservation is a unilateral statement through which a state seeks to exclude or modify the legal effect of certain treaty provisions in their application to that state. Reservations are subject to the rules of the particular treaty and international treaty law.

Can a state withdraw from a treaty?

Sometimes. Withdrawal may be permitted by the treaty itself or under applicable international law. A state cannot necessarily withdraw whenever it wishes.

Can a treaty be terminated?

Yes. Treaties may be terminated according to their provisions or under recognized grounds in international law, including certain forms of material breach or other circumstances established by treaty law.

What happens when a state violates a treaty?

A treaty violation can result in international responsibility. Depending upon the circumstances, the consequences may include diplomatic measures, dispute settlement, suspension of certain obligations, or other remedies recognized by international law.

Can domestic law override an international treaty?

As a general principle of international law, a state cannot invoke its domestic law as justification for failing to perform an international obligation. However, the domestic legal effect of a treaty depends upon the constitutional system of the state concerned.

Can a treaty violate international law?

Yes. Treaty-making is subject to international legal limitations. In particular, a treaty cannot validly derogate from a peremptory norm of general international law (jus cogens).

What is pacta sunt servanda?

Pacta sunt servanda is the principle that treaties in force are binding upon their parties and must be performed in good faith.

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Conclusion

Treaties are the principal instruments through which states deliberately create detailed and legally binding international obligations.

Their importance extends far beyond formal diplomacy. Treaties establish institutions, regulate international relations, protect human rights, govern economic and environmental cooperation, settle territorial questions, regulate armed conflict, and provide mechanisms for resolving international disputes.

The law of treaties also demonstrates the distinctive nature of the international legal system. There is no universal legislature that automatically imposes every international rule upon every state. Instead, sovereign states participate in a legal process through which agreements are negotiated, adopted, accepted, interpreted, performed, amended, and, where legally justified, terminated.

The Vienna Convention on the Law of Treaties provides the central framework for understanding this process.

Ultimately, the significance of a treaty lies in the transformation of international agreement into legal obligation. A state may negotiate because of political interests, economic necessity, security concerns, or diplomatic compromise, but once it has validly undertaken a treaty obligation, the agreement enters the realm of international law.

That transformation—from agreement to obligation—is one of the fundamental mechanisms through which the modern international legal order operates.