A treaty is an international agreement between sovereign states or other subjects of international law (including international organizations) that is governed by international law.https://treaties.un.org/doc/source/publications/thb/english.pdf International Treaties. A treaty may also be known as an international agreement, protocol, covenant, convention, pact, or exchange of letters, among other terms. However, only documents that are legally binding on the parties are considered treaties under international law.Shaw, Malcolm. (2003). In United States constitutional law, the term "treaty" has a special meaning which is more restricted than its meaning in international law; see United States law below. Treaties may be bilateral (between two parties) or multilateral (involving more than two parties).
International agreements were used in some form by most major civilizations and became increasingly common and more sophisticated during the early modern era. The early 19th century saw developments in diplomacy, foreign policy, and international law reflected by the widespread use of treaties. In the 20th century, the Vienna Convention on the Law of Treaties (VCLT) codified these practices by establishing rules for creating, amending, interpreting, and terminating treaties; and for resolving disputes and alleged breaches.
Treaties serve as primary sources of international law and have codified or established many international legal principles since the early 20th century. As with other sources of international law, they are only binding on the parties that have signed and ratified them. In certain conditions a treaty may also be invalidated and thus rendered unenforceable, for example, if it violates a peremptory norm (jus cogens) such as permitting a war of aggression or crimes against humanity.Vienna Convention on the Law of Treaties, Article 53, May 23, 1969, 1155 U.N.T.S 331, 8 International Legal Materials 679 (1969)
Treaties are not required to follow any standard form and differ widely in substance and complexity. They are applied to wide range of subject matters such as security, trade, environment, and human rights. Treaties are also used to establish governance frameworks for international institutions such as the International Criminal Court and the United Nations.
Governance of treaties under international law
Role of the United Nations The United Nations has extensive power to convene states to enact large-scale multilateral treaties and has experience doing so. Under the United Nations Charter, which is itself a treaty, treaties must be registered with the UN to be invoked before it, or enforced in its judiciary organ, the International Court of Justice. This was done to prevent the practice of secret treaties, which proliferated in the 19th and 20th centuries and often precipitated or exacerbated conflict. Article 103 of the Charter also states that its members' obligations under the Charter outweigh any competing obligations under other treaties.
After their adoption, treaties, as well as their amendments, must follow the official legal procedures of the United Nations, as applied by the Office of Legal Affairs, including signature, ratification and entry into force.
Vienna Convention on the Law of Treaties
The Vienna Convention on the Law of Treaties (VCLT) is an international agreement governing treaties between states.Vienna Convention on the Law of Treaties, pg. 1 Its provisions cover the lifecycle of treaties including how they are negotiated, interpreted, amended and terminated. It also contains provisions governing the resolution of disputes and alleged breaches.
The VCLT was originally drafted by the International Law Commission, and was adopted on 22 May 1969. In entered into force on 27 January 1980 and, as at May 2026, has been ratified by 119 countries Non-ratifying parties, such as the United States, have recognized parts of the VCLT as restating customary international law.
Treaty forms
Types of treaties
Bilateral and multilateral treaties Bilateral treaties are concluded between two states or entities.Nicolson, Harold. (1934). Diplomacy, p. 135. It is possible for a bilateral treaty to have more than two parties; for example, each of the bilateral treaties between Switzerland and the European Union (EU) has seventeen parties: The parties are divided into two groups, the Swiss ("on the one part") and the EU and its member states ("on the other part"). The treaty establishes rights and obligations between the Swiss and the EU and the member states severally—it does not establish any rights and obligations amongst the EU and its member states.
A multilateral treaty is concluded among several countries, establishing rights and obligations between each party and every other party. Multilateral treaties may be regional or may involve states across the world. Treaties of "mutual guarantee" are international compacts, e.g., the Treaty of Locarno which guarantees each signatory against attack from another.
Non-binding agreements Signing a treaty implies a recognition that the other side is a sovereign state and that the agreement being considered is enforceable under international law. Hence, states can be very careful about describing an agreement with another party as a treaty. For example, within the United States, agreements between states are compacts and agreements between states and the federal government or between agencies of the government are memoranda of understanding.
Another situation can occur when one party wishes to create an obligation under international law, but the other party does not. This factor has been at work with respect to discussions between North Korea and the United States over security guarantees and nuclear proliferation.
Treaty structure There is no prescribed form that a treaty must take to have binding effect. However, since the late 19th century, most treaties have followed a fairly consistent format. A treaty typically begins with a preamble describing the "High Contracting Parties" and their shared objectives in executing the treaty, as well as summarizing any underlying events (such as the aftermath of a war in the case of a peace treaty). In the Geneva Conventions, the term "High Contracting Parties" refers to the states that have joined the conventions and are therefore bound to uphold them. Modern preambles are sometimes structured as a single very long sentence formatted into multiple paragraphs for readability, in which each of the paragraphs begins with a gerund (desiring, recognizing, having, etc.).
The High Contracting Parties—referred to as either the official title of the head of state (but not including the personal name), e.g. His Majesty The King of X or His Excellency The President of Y, or alternatively in the form of " Government of Z"—are enumerated, along with the full names and titles of their plenipotentiary representatives; a boilerplate clause describes how each party's representatives have communicated (or exchanged) their "full powers" (i.e., the official documents appointing them to act on behalf of their respective high contracting party) and found them in good or proper form. However, under the Vienna Convention on the Law of Treaties if the representative is the head of state, head of government or minister of foreign affairs, no special document is needed, as holding such high office is sufficient.
The end of the preamble and the start of the actual agreement is often signaled by the words "have agreed as follows".
After the preamble comes numbered articles, which contain the substance of the parties' actual agreement. Each article heading usually encompasses a paragraph. A long treaty may further group articles under chapter headings.
Modern treaties, regardless of subject matter, usually contain articles governing where the final authentic copies of the treaty will be deposited and how any subsequent disputes as to their interpretation will be peacefully resolved.
The end of a treaty, the eschatocol (or closing protocol), is often signaled by language such as "in witness whereof" or "in faith whereof", followed by the words "DONE at", then the site(s) of the treaty's execution and the date(s) of its execution. The date is typically written in its most formal, non-numerical form; for example, the Charter of the United Nations reads "DONE at the city of San Francisco the twenty-sixth day of June, one thousand nine hundred and forty-five". If applicable, a treaty will note that it is executed in multiple copies in different languages, with a stipulation that the versions in different languages are equally authentic.
The signatures of the parties' representatives follow at the very end. When the text of a treaty is later reprinted, such as in a collection of treaties currently in effect, an editor will often append the dates on which the respective parties ratified the treaty and on which it came into effect for each party.
Formation
Consent to be bound A state must express its consent to be bound to a treaty, for example, through signature, ratification, acceptance, approval or accession.
Signature A signature can serve two different functions in treaty negotiations. If a state's representative has been authorised in advance, their signature can express consent and immediately bind the state as a legal party. More commonly, however, a signature will serve to authenticate the text of the treaty but consent to be bound will be subject to future ratification.
Ratification, acceptance or approval Ratification is process through which a country expresses its consent to be bound to a treaty's provisions by implementing them domestically, for example, through legislation or executive order. This provides a deliberate gap between when a treaty is negotiated and signed, and when it is enacted into domestic law.
Where a treaty states that it will be enacted through ratification, acceptance or approval, the parties must sign to indicate acceptance of the wording but there is no requirement on a state to later ratify the treaty, although they may still be subject to certain obligations. In some jurisdictions, such as the United States, a treaty is defined specifically as an international agreement that has been ratified, and thus made binding per the procedures established under domestic law.
Multilateral treaties will often delay entry into force until a minimum number of signatories have ratified the treaty.
Accession Accession refers to a state choosing to become party to a treaty that it is unable to sign, such as when joining an already established regional body.
Reservations
Reservations are essentially caveats to a state's acceptance of a treaty. A state can make a reservation in the form of a unilateral statement to exclude or to modify the legal obligation and its effects on the reserving state.Vienna Convention on the Law of Treaties, Article 2 Sec. 1(d) Text of the Convention These must be included at the time of signing or ratification; a party cannot add a reservation after it has already joined a treaty. Reservations can have one of three effects: the reserving state is bound by the treaty but the effects of the relevant provisions are precluded or changed, the reserving state is bound by the treaty but not the relevant provisions, or the reserving state is not bound by the treaty.
Originally, international law was unaccepting of treaty reservations, rejecting them unless all parties to the treaty accepted the same reservations. However, in the interest of encouraging the largest number of states to join treaties, a more permissive rule regarding reservations has emerged. While some treaties still expressly forbid any reservations, they are now generally permitted to the extent that they are not inconsistent with the goals and purposes of the treaty.