In This Article Expand or collapse the "in this article" section Unilateral Acts

  • Introduction
  • General Overviews
  • International Organizations and Unilateral Acts
  • Reciprocal Conducts of States
  • The Unilateral Acts of the States in the International Law Commission
  • Typology
  • The Optional Clause
  • Capacity of State Authorities to Make Unilateral International Commitments
  • Rules and Methods of Interpretation
  • Basis and Binding Nature
  • Modification and Revocation
  • Selected Cases

International Law Unilateral Acts
Francisco Jiménez García
  • LAST REVIEWED: 18 July 2017
  • LAST MODIFIED: 25 October 2017
  • DOI: 10.1093/obo/9780199796953-0116


May the representatives of states undertake commitments unilaterally and thus limit their freedom to act? Are unilateral acts as an independent source of international obligations possible in a legal system based on consensualism and in the principle of pacta sunt servanda? Are the subjects of the decentralized international community entitled to rely on such unilateral declarations and to require that such obligations be respected under the principles of good faith and legitimate expectations? What should be the requirements and conditions necessary to affirm the existence of such acts? How would such statements have to be interpreted, and can they be revoked or modified? These would be the main questions of the debate about the legal effects of unilateral acts and their consequences, and the dispute between those who confirm its legal validity and those who question it or deny its autonomous nature in the face of other regulatory processes. In order to define the scope of study, we must differentiate between those unilateral declarations or acts involved in the various regulatory processes (conventional, customary, and institutional) and those unilateral acts that have enough capacity to create, autonomously and independently, legal obligations to their authors and rights to third parties or to the international community as a whole, depending on the principles of good faith and legitimate expectations. The criterion of material autonomy becomes the defining element of such acts because the (potential) legality of the unilateral act is justified in itself and does not depend on its adequacy or conformity with other international enabling norms or rules. Unilateral acts do not create international norms for themselves, but they can have sufficient capacity to create legal obligations if this is the clear and unequivocal will of the state in this regard. Such acts represent an exception to the established principle of pacta sunt servanda and to the conception of the international regulatory system as a result of a process or consensus to become a unilateral procedure for the creation of international obligations (acta sunt servanda). For this reason, unilateral acts in a strict sense differ from unilateral acts subject to the general system of the law of treaties (acts of authentication and manifestation of consent to be bound by a treaty, reserves, interpretative declarations, treaty denunciation or withdrawal, etc.), from the executive acts of binding or generally accepted international rules (maritime delimitations, for example), and from various unilateral acts that can integrate the regulatory process of a customary norm as precedent or evidence of the opinio iuris. Despite the existence of previous case law, practice, and doctrine, the judgments delivered in the cases concerning nuclear tests and resolved by the International Court of Justice on 20 December 1974 are used as the point of reference for the production of the general doctrine of unilateral acts. This case law was reiterated by the Court of The Hague and other international jurisdictions.

General Overviews

There is a relevant bibliography that has developed a general doctrine of unilateral acts. From the first studies (Suy 1962, Dehaussy 1965, Gigante 1969) to literature that emerged after the judgments in the nuclear tests cases (International Court of Justice 1974, cited under Selected Cases) and the work of the International Law Commission (ILC) on this topic (ILC 1996–2006), the authors have investigated the basis and the legal nature of such acts, as well as the need to determine and define their relationships with other institutions and legal principles. See also Suy 2007, Rubin 1977, Sicault 1979, Degan 1997, Charpentier 1996, Zemanek 1998, and Kassoti 2015.

  • Charpentier, Jean. “Engagements unilatéraux et engagements conventionnels: Différences et convergences.” In Theory of International Law at the Threshold of the 21st Century: Essays in Honour of Krzysztof Skubiszewski. Edited by Jerzy Makarczyk, 367–380. The Hague: Kluwer Law International, 1996.

    This work stresses the element of autonomy as an essential characteristic of unilateral acts. The author maintains that the legal value of unilateral acts derives from its own characteristics in terms of manifestation of will or consent of the author to assume legal obligations under international law.

  • Degan, Vladimir Duro. Sources of International Law. The Hague: Martinus Nijhoff, 1997.

    For the author there is no peremptory norm of general international law precluding sovereign states from assuming legal obligations even unilaterally. He distinguishes unilateral acts only in form (particularly within the treaty-making and treaty-executing processes) and autonomous acts. He specifies the conditions of the validity and various categories of unilateral acts in relation to international law (pp. 253–338). See also his “Unilateral Act as a Source of Particular International Law” in Finnish Yearbook of International Law 5 (1994): 149–266.

  • Dehaussy, Jacques. “Les actes juridiques unilatéraux en droit international public: À propos d’une théorie restrictive.” Journal du Droit International 92 (1965): 41–66.

    This article focuses on the critical analysis of the work of Eric Suy (Suy 1962) on unilateral acts, which Dehaussy describes as restrictive. The author proposes an extensive theory with respect to the various elements of the unilateral acts examined.

  • Gigante, A. “The Effect of Unilateral State Acts in International Law.” New York University Journal of International Law and Politics 2 (1969): 333–362.

    Taking as reference the municipal law unilateral contracts, this study develops a general theory of unilateral acts taken years later in the nuclear tests cases (International Court of Justice 1974, cited under Selected Cases). In the framework of the concepts of estoppel and acquiescence, the author claims the consistency of state action to support the binding nature of unilateral acts.

  • Kassoti, Eva. The Juridical Nature of Unilateral Acts of States in International Law. Queen Mary Studies in International Law 20. Boston and Leiden, The Netherlands: Brill Nijhoff, 2015.

    DOI: 10.1163/9789004300767

    The author explores the question of the legal nature of unilateral acts by focusing on their essential characteristics. She focuses on the element of autonomy by presenting the contextual indicators: absence of the treaty law context, absence of a rule that requires reciprocity, and absence of a pattern of offer/acceptance. She also analyzes the criterion distinguishing between unilateral juridical acts and unilateral politics acts to finish a brief excursus on unilateral declarations of independence.

  • Rubin, Alfred P. “The International Legal Effects of Unilateral Declarations.” American Journal International Law 71.1 (1977): 1–30.

    DOI: 10.2307/2200323

    This author makes a critical analysis of the judgments of the International Court of Justice on the nuclear tests cases (International Court of Justice 1974, cited under Selected Cases). He analyzes the past practice and the existing doctrine about the ability of unilateral declarations to generate autonomously legal obligations beyond the maxim pacta sunt servanda. In his analysis he contrasts the different kinds of unilateral statements and similar figures (estoppel).

  • Sicault, Jean Didier. “Du caractère obligatoire des engagements unilatéraux en droit international public.” Revue Général de Droit International Public 83 (1979): 633–688.

    Sicault defends the institution of unilateral acts as the autonomous source of international obligations in accordance with the requirements established on the nuclear tests cases. He discusses the interpretation, revocation, and modification of unilateral obligations and advocates the principle of good faith as the foundation of the obligatory nature of the unilateral commitments.

  • Suy, Eric. Les actes juridiques unilatéraux en droit international public. Paris: Librairie Général de Droit et de Jurisprudence, 1962.

    This is one of the first works that develops a general theory on unilateral acts in international law. The author defends the existence in international law of strictly unilateral promises with binding effect on the basis of the customary rule that international engagements must be respected. He focuses on the traditionally formalized unilateral acts and their role in the formation of custom.

  • Suy, Eric. “Unilateral Acts of States as a Source of International Law: Some New Thoughts and Frustrations.” In Droit du pouvoir, pouvoir du droit: Mélanges offerts à Jean Salmon. By Olivier Corten, Pierre Klein, Anne Lagerwall, et al., 631–642. Brussels: Bruylant, 2007.

    In this work, Suy makes some new comments, in particular about autonomy. He focuses on the statements of states in accordance with certain treaties or treaty provisions (e.g., France’s acceptance of the Non-proliferation Treaty prior to its accession or the Soviet Union’s declaration before the General Assembly that they would not be the first to use nuclear weapons). See pp. 631–642.

  • Zemanek, Karl. “Unilateral Legal Acts Revisited.” In International Law: Theory and Practice; Essays in Honour of Eric Suy. Edited by Karel Wellens, 209–221. The Hague: Martinus Nijhoff, 1998.

    The author focuses on the relationship of unilateral acts with the treaty-making process and on the custom-forming process to conclude with an analysis of the autonomous and legally binding character of unilateral acts as a source of international obligation. He also points out the capacity of the authority to bind the state by a unilateral declaration.

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