The Concept of an Agreement in International Law
The concept of agreement in international law is central to the formation of legal relationships, yet the legal system provides no single, authoritative account of what constitutes an agreement. Unlike treaties, whose formation is governed by detailed rules under the VCLT, the broader category of agreement, whether binding or non-binding, treaty or non-treaty, is scattered across disparate doctrines and case law. Some of the requirements for agreement can only be inferred from the law of treaties.
This article aims not to propose a new functional theory, but to identify and clarify the underlying elements that recur across these sources and give content to the idea of agreement in international law. Through an analysis of treaties, memoranda of understanding, joint statements, minutes, and even informal arrangements, it seeks to distill the common features that characterize an agreement: the conclusion of an intentional and mutual acceptance of a precise and certain idem between actors empowered to agree on behalf of participants in international law. These elements, drawn from practice, offer a working framework for determining when an agreement exists under international law.
The need for such a framework is increasingly pressing. As states and international actors adopt varied forms of cooperation outside traditional treaty-making, the line between binding and non-binding instruments, and between agreements and unilateral acts, has blurred. As a result, it is becoming increasingly difficult to navigate disparate communications and identify when parties have agreed. Clarifying the basic elements of agreement allows legal actors, adjudicators, and scholars to speak more precisely about when agreement arises and when it does not.
Recommended Citation: William Thomas Worster, The Concept of an Agreement in International Law, 49 Fordham Int'l L.J. 1093 (2026).