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 sub regional instruments entered into under its framework are called agreements.
Source: Treaties Office Database