A treaty is a legally binding international agreement governed by international law. Under Article 2 of the 1969 Vienna Convention on the Law of Treaties, the term treaty means an international agreement concluded between states in written form and governed by international law, whether contained in one instrument or several related instruments and regardless of the particular designation used. This definition is important because international instruments can have many names, including treaty, agreement, convention, protocol, charter, covenant or pact.
The name alone does not determine the legal character of the instrument. What matters is whether the parties intended to create international legal obligations and whether the relevant legal requirements are satisfied. The United Nations Treaty Collection likewise explains that international practice uses many different titles and that nomenclature does not provide a precise universal classification.
Treaties can be bilateral or multilateral. A bilateral treaty involves two parties, normally two states, while a multilateral treaty involves three or more parties. Treaties can address almost any subject capable of international regulation, including peace, borders, trade, investment, taxation, extradition, human rights, environmental protection, arms control, transportation and international institutions. Some treaties establish detailed reciprocal obligations, while others establish broad frameworks within which subsequent decisions or protocols operate. A treaty can also establish an international organisation.
The United Nations Charter is itself an international treaty and functions as the founding instrument of the United Nations. It establishes the organisation's purposes, principles, membership arrangements and principal organs. The Charter therefore illustrates how a treaty can do more than regulate a single transaction between states.
Treaty making generally involves several stages, although the exact procedure depends upon the instrument and the constitutional systems of the participating states. States may first negotiate and adopt a text. The text may then be authenticated and signed. Signature can express consent to be bound in some circumstances, but many treaties require a further act such as ratification, acceptance or approval. A state can also become a party through accession where the treaty permits that procedure.
The Vienna Convention defines ratification, acceptance, approval and accession as international acts through which a state establishes its consent to be bound. Entry into force occurs according to the treaty's provisions or according to applicable international rules. A signature therefore does not automatically mean that every treaty obligation has immediately become legally binding in the same way for every state.
A fundamental principle of treaty law is that treaties in force are to be performed in good faith. The Vienna Convention expresses this through the principle commonly known as pacta sunt servanda. It also establishes rules concerning interpretation, amendment, modification, invalidity, termination and suspension. Treaty obligations therefore exist within a legal framework rather than as informal political promises.
Interpretation is particularly important because disputes can arise about the meaning of words, the relationship between provisions and the circumstances in which a treaty was concluded. The Vienna Convention provides general interpretative rules intended to promote consistent legal analysis. States can also negotiate amendments or modifications where the treaty and applicable international law permit them. The legal character of a treaty therefore continues beyond signature and includes a body of rules governing how obligations operate over time.
Treaties can contain different types of obligations. Some create reciprocal commitments in which each party undertakes obligations in exchange for corresponding obligations by others. Others establish objective standards that parties agree to maintain. Human rights treaties, for example, can establish obligations concerning the treatment of persons under a state's jurisdiction. Environmental treaties can establish emissions, conservation, reporting or cooperation obligations. Boundary treaties can define territorial limits. Institutional treaties can establish organisations, organs, voting systems and procedures.
A treaty can also contain reservations, which are unilateral statements made when signing, ratifying, accepting, approving or acceding through which a state purports to exclude or modify the legal effect of particular provisions in their application to that state, subject to the treaty and international law. The possibility of reservations demonstrates that participation in a multilateral treaty can sometimes involve different legal positions among participating states.
Treaties should not be confused with every political promise made between governments. An official statement or joint declaration may have political significance without necessarily creating the same type of legal obligation as a treaty. Conversely, the title of an instrument does not determine whether it is legally binding. The UN Treaty Collection explains that instruments called agreements, conventions, protocols, exchanges of notes and other names can fall within international treaty law if the necessary characteristics are present.
The legal intention of the parties, the content of the instrument and the applicable rules are therefore more important than the title on the front page. Some memoranda of understanding may be politically or administratively important but not intended to create treaty obligations, while another instrument with a less formal title can create binding international obligations. Classification must consequently be based on substance and legal intention rather than terminology alone.
Treaty registration and publication contribute to transparency in international relations. Article 102 of the United Nations Charter requires every treaty and international agreement entered into by a UN Member State after the Charter came into force to be registered with the Secretariat and published as soon as possible. The United Nations Treaty Series contains treaties and international agreements registered or filed and recorded by the Secretariat. Registration does not itself create the legal obligation.
Rather, the obligation arises from the agreement and applicable international law, while registration serves transparency and publication purposes. The Charter also contains a specific rule concerning reliance on an unregistered treaty or international agreement before a UN organ. The registration system therefore provides a public institutional record of international legal instruments and their participating states.
A treaty is consequently a formal category of international legal agreement rather than simply a diplomatic document with a particular title. It is an instrument through which states or, under relevant legal frameworks, international organisations can establish rights and obligations governed by international law. Treaties can be bilateral or multilateral, narrow or comprehensive, temporary or continuing, technical or constitutional in character.
Their creation can involve negotiation, adoption, signature, ratification, acceptance, approval or accession, followed by entry into force according to specified conditions. Once operative, treaties are interpreted, performed, amended and terminated under international law. The term is broad enough that many instruments called agreements or conventions may also constitute treaties in the generic legal sense. The Vienna Convention on the Law of Treaties provides the central codified framework for treaty relations between states, while customary international law and other relevant rules also form part of the wider law governing international agreements.
