Definition of key terms used in the UN Treaty Collection
Exchange of Notes
Memoranda of Understanding
Signatories and Parties
This introductory note seeks to provide a basic - but not an exhaustive - overview of the key
terms employed in the United Nations Treaty Collection to refer to international instruments
binding at international law: treaties, agreements, conventions, charters, protocols, declarations,
memoranda of understanding, modus vivendi and exchange of notes. The purpose is to facilitate a
general understanding of their scope and function.
Over the past centuries, state practice has developed a variety of terms to refer to
international instruments by which states establish rights and obligations among themselves. The
terms most commonly used are the subject of this overview. However, a fair number of additional
terms have been employed, such as "statutes", "covenants", "accords" and others. In spite of this
diversity of terminology, no precise nomenclature exists. In fact, the meaning of the terms used is
variable, changing from State to State, from region to region and instrument to instrument. Some of
the terms can easily be interchanged: an instrument that is designated "agreement" might also be
The title assigned to such international instruments thus has normally no overriding legal
effects. The title may follow habitual uses or may relate to the particular character or importance
sought to be attributed to the instrument by its parties. The degree of formality chosen will depend
upon the gravity of the problems dealt with and upon the political implications and intent of the
Although these instruments differ from each other by title, they all have common features
and international law has applied basically the same rules to all of these instruments. These rules are
the result of long practice among the States, which have accepted them as binding norms in their
mutual relations. Therefore, they are regarded as international customary law. Since there was a
general desire to codify these customary rules, two international conventions were negotiated. The
1969 Vienna Convention on the Law of Treaties ("1969 Vienna Convention"), which entered into
force on 27 January 1980, contains rules for treaties concluded between States. The 1986 Vienna
Convention on the Law of Treaties between States and International Organizations or between
International Organizations ("1986 Vienna Convention"), which has still not entered into force,
added rules for treaties with international organizations as parties. Both the 1969 Vienna Convention
and the 1986 Vienna Convention do not distinguish between the different designations of these
instruments. Instead, their rules apply to all of those instruments as long as they meet certain
Article 102 of the Charter of the United Nations provides that "every treaty and every
international agreement entered into by any Member State of the United Nations after the present
Charter comes into force shall as soon as possible be registered with the Secretariat and published
by it". All treaties and international agreements registered or filed and recorded with the Secretariat
since 1946 are published in the UNTS. By the terms "treaty" and "international agreement", referred
to in Article 102 of the Charter, the broadest range of instruments is covered. Although the General
Assembly of the UN has never laid down a precise definition for both terms and never clarified their
mutual relationship, Art.1 of the General Assembly Regulations to Give Effect to Article 102 of the
Charter of the United Nations provides that the obligation to register applies to every treaty or
international agreement "whatever its form and descriptive name". In the practice of the Secretariat
under Article 102 of the UN Charter, the expressions "treaty" and "international agreement" embrace
a wide variety of instruments, including unilateral commitments, such as declarations by new
Member States of the UN accepting the obligations of the UN Charter, declarations of acceptance
of the compulsory jurisdiction of the International Court of Justice under Art.36 (2) of its Statute and
certain unilateral declarations that create binding obligations between the declaring nation and other
nations. The particular designation of an international instrument is thus not decisive for the
obligation incumbent on the Member States to register it.
It must however not be concluded that the labelling of treaties is haphazard or capricious.
The very name may be suggestive of the objective aimed at, or of the accepted limitations of action
of the parties to the arrangement. Although the actual intent of the parties can often be derived from
the clauses of the treaty itself or from its preamble, the designated term might give a general
indication of such intent. A particular treaty term might indicate that the desired objective of the
treaty is a higher degree of cooperation than ordinarily aimed for in such instruments. Other terms
might indicate that the parties sought to regulate only technical matters. Finally, treaty terminology
might be indicative of the relationship of the treaty with a previously or subsequently concluded
(b) Treaty as a specific term: There are no consistent rules when state practice employs the
terms "treaty" as a title for an international instrument. Usually the term "treaty" is reserved for
matters of some gravity that require more solemn agreements. Their signatures are usually sealed
and they normally require ratification. Typical examples of international instruments designated as
"treaties" are Peace Treaties, Border Treaties, Delimitation Treaties, Extradition Treaties and
Treaties of Friendship, Commerce and Cooperation. The use of the term "treaty" for international
instruments has considerably declined in the last decades in favor of other terms.
The term "agreement" can have a generic and a specific meaning. It also has acquired a
special meaning in the law of regional economic integration.
(a) Agreement as a generic term: The 1969 Vienna Convention on the Law of Treaties
employs the term "international agreement" in its broadest sense. On the one hand, it defines treaties
as "international agreements" with certain characteristics. On the other hand, it employs the term
"international agreements" for instruments, which do not meet its definition of "treaty". Its Art.3
refers also to "international agreements not in written form". Although such oral agreements may
be rare, they can have the same binding force as treaties, depending on the intention of the parties.
An example of an oral agreement might be a promise made by the Minister of Foreign Affairs of one
State to his counterpart of another State. The term "international agreement" in its generic sense
consequently embraces the widest range of international instruments.
(b) Agreement as a particular term: "Agreements" are usually less formal and deal with a
narrower range of subject-matter than "treaties". There is a general tendency to apply the term
"agreement" to bilateral or restricted multilateral treaties. It is employed especially for instruments
of a technical or administrative character, which are signed by the representatives of government
departments, but are not subject to ratification. Typical agreements deal with matters of economic,
cultural, scientific and technical cooperation. Agreements also frequently deal with financial
matters, such as avoidance of double taxation, investment guarantees or financial assistance. The UN
and other international organizations regularly conclude agreements with the host country to an
international conference or to a session of a representative organ of the Organization. Especially in
international economic law, the term "agreement" is also used as a title for broad multilateral
agreements (e.g. the commodity agreements). The use of the term "agreement" slowly developed
in the first decades of this century. Nowadays by far the majority of international instruments are
designated as agreements.
(c) Agreements in regional integration schemes: Regional integration schemes are based
on general framework treaties with constitutional character. International instruments which amend
this framework at a later stage (e.g. accessions, revisions) are also designated as "treaties".
Instruments that are concluded within the framework of the constitutional treaty or by the organs of
the regional organization are usually referred to as "agreements", in order to distinguish them from
the constitutional treaty. For example, whereas the Treaty of Rome of 1957 serves as a quasi-constitution of the European Community, treaties concluded by the EC with other nations are usually
designated as agreements. Also, the Latin American Integration Association (LAIA) was established
by the Treaty of Montevideo of 1980, but the subregional instruments entered into under its
framework are called agreements.
The term "charter" is used for particularly formal and solemn instruments, such as the
constituent treaty of an international organization. The term itself has an emotive content that goes
back to the Magna Carta of 1215. Well-known recent examples are the Charter of the United Nations
of 1945 and the Charter of the Organization of American States of 1952.
The term "convention" again can have both a generic and a specific meaning.
(a) Convention as a generic term: Art.38 (1) (a) of the Statute of the International Court of
Justice refers to "international conventions, whether general or particular" as a source of law, apart
from international customary rules and general principles of international law and - as a secondary source - judicial decisions and the teachings of the most highly qualified publicists. This generic use of
the term "convention" embraces all international agreements, in the same way as does the generic
term "treaty". Black letter law is also regularly referred to as "conventional law", in order to
distinguish it from the other sources of international law, such as customary law or the general
principles of international law. The generic term "convention" thus is synonymous with the generic
(b) Convention as a specific term: Whereas in the last century the term "convention" was
regularly employed for bilateral agreements, it now is generally used for formal multilateral treaties
with a broad number of parties. Conventions are normally open for participation by the international
community as a whole, or by a large number of states. Usually the instruments negotiated under the
auspices of an international organization are entitled conventions (e.g. Convention on Biological
Diversity of 1992, United Nations Convention on the Law of the Sea of 1982, Vienna Convention
on the Law of Treaties of 1969). The same holds true for instruments adopted by an organ of an
international organization (e.g. the 1951 ILO Convention concerning Equal Remuneration for Men
and Women Workers for Work of Equal Value, adopted by the International Labour Conference or
the 1989 Convention on the Rights of the Child, adopted by the General Assembly of the UN).
The term "declaration" is used for various international instruments. However, declarations
are not always legally binding. The term is often deliberately chosen to indicate that the parties do
not intend to create binding obligations but merely want to declare certain aspirations. An example
is the 1992 Rio Declaration. Declarations can however also be treaties in the generic sense intended
to be binding at international law. It is therefore necessary to establish in each individual case
whether the parties intended to create binding obligations. Ascertaining the intention of the parties
can often be a difficult task.
Some instruments entitled "declarations" were not originally intended to have binding force,
but their provisions may have reflected customary international law or may have gained binding character as customary law at a later stage. Such was
the case with the 1948 Universal Declaration of Human Rights.
Declarations that are intended to have binding effects could be classified as follows:
(a) A declaration can be a treaty in the proper sense. A significant example is the Joint
Declaration between the United Kingdom and China on the Question of Hong Kong of 1984.
(b) An interpretative declaration is an instrument that is annexed to a treaty with the goal
of interpreting or explaining the provisions of the latter.
(c) A declaration can also be an informal agreement with respect to a matter of minor
(d) A series of unilateral declarations can constitute binding agreements. A typical example
are declarations under the Optional Clause of the Statute of the International Court of Justice that
create legal bonds between the declarants, although not directly addressed to each other. Another
example is the unilateral Declaration on the Suez Canal and the arrangements for its operation issued
by Egypt in 1957 which was considered to be an engagement of an international character.
Exchange of Notes
An "exchange of notes" is a record of a routine agreement, that has many similarities with
the private law contract. The agreement consists of the exchange of two documents, each of the
parties being in the possession of the one signed by the representative of the other. Under the usual
procedure, the accepting State repeats the text of the offering State to record its assent. The
signatories of the letters may be government Ministers, diplomats or departmental heads. The
technique of exchange of notes is frequently resorted to, either because of its speedy procedure, or,
sometimes, to avoid the process of legislative approval.
Memoranda of Understanding
A memorandum of understanding is an international instrument of a less formal kind. It
often sets out operational arrangements under a framework international agreement. It is also used
for the regulation of technical or detailed matters. It is typically in the form of a single instrument
and does not require ratification. They are entered into either by States or International
Organizations. The United Nations usually concludes memoranda of understanding with Member
States in order to organize its peacekeeping operations or to arrange UN Conferences. The United
Nations also concludes memoranda of understanding on cooperation with other international
A modus vivendi is an instrument recording an international agreement of temporary or
provisional nature intended to be replaced by an arrangement of a more permanent and detailed
character. It is usually made in an informal way, and never requires ratification.
The term "protocol" is used for agreements less formal than those entitled "treaty" or
"convention". The term could be used to cover the following kinds of instruments:
(a) A Protocol of Signature is an instrument subsidiary to a treaty, and drawn up by the
same parties. Such a Protocol deals with ancillary matters such as the interpretation of particular
clauses of the treaty, those formal clauses not inserted in the treaty, or the regulation of technical
matters. Ratification of the treaty will normally ipso facto involve ratification of such a Protocol.
(b) An Optional Protocol to a Treaty is an instrument that establishes additional rights and
obligations to a treaty. It is usually adopted on the same day, but is of independent character and
subject to independent ratification. Such protocols enable certain parties of the treaty to establish
among themselves a framework of obligations which reach further than the general treaty and to
which not all parties of the general treaty consent, creating a "two-tier system". The Optional
Protocol to the International Covenant on Civil and Political Rights of 1966 is a well-known
(c) A Protocol based on a Framework Treaty is an instrument with specific substantive
obligations that implements the general objectives of a previous framework or umbrella convention.
Such protocols ensure a more simplified and accelerated treaty-making process and have been used
particularly in the field of international environmental law. An example is the 1987 Montreal
Protocol on Substances that Deplete the Ozone Layer adopted on the basis of Arts.2 and 8 of the
1985 Vienna Convention for the Protection of the Ozone Layer.
(d) A Protocol to amend is an instrument that contains provisions that amend one or various
former treaties, such as the Protocol of 1946 amending the Agreements, Conventions and Protocols
on Narcotic Drugs.
(e) A Protocol as a supplementary treaty is an instrument which contains supplementary
provisions to a previous treaty, e.g. the 1967 Protocol relating to the Status of Refugees to the 1951
Convention relating to the Status of Refugees.
(f) A Proces-Verbal is an instrument that contains a record of certain understandings arrived
at by the contracting parties.
Signatories and Parties
The term “Parties", which appears in the header of each treaty, in the publication Multilateral Treaties Deposited with the Secretary-General, includes both "Contracting States" and "Parties". For general reference, the term "Contracting States" refers to States and other entities with treaty-making capacity which have expressed their consent to be bound by a treaty where the treaty has not yet entered into force or where it has not entered into force for such States and entities; the term "Parties" refers to States and other entities with treaty-making capacity which have expressed their consent to be bound by a treaty and where the treaty is in force for such States and entities.)
The term "treaty" can be used as a common generic term or as a particular term which
indicates an instrument with certain characteristics.
(a) Treaty as a generic term: The term "treaty" has regularly been used as a generic term
embracing all instruments binding at international law concluded between international entities,
regardless of their formal designation. Both the 1969 Vienna Convention and the 1986 Vienna
Convention confirm this generic use of the term "treaty". The 1969 Vienna Convention defines a
treaty as "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". The 1986 Vienna Convention extends the definition of treaties
to include international agreements involving international organizations as parties.
In order to speak of a "treaty" in the generic sense, an instrument has to meet various
criteria. First of all, it has to be a binding instrument, which means that the contracting parties
intended to create legal rights and duties. Secondly, the instrument must be concluded by states or
international organizations with treaty-making power. Thirdly, it has to be governed by international
law. Finally the engagement has to be in writing. Even before the 1969 Vienna Convention on the
Law of Treaties, the word "treaty" in its generic sense had been generally reserved for engagements
concluded in written form.