¹ See, e.g., Richard Falk, Foreword, in Essays on Espionage and international Law v, v (Roland J. Stranger ed., 1962) (“Traditional international law is remarkably oblivious to the peacetime practice of espionage. Leading treatises overlook espionage altogether or contain a perfunctory paragraph that defines a spy and describes his hapless fate upon capture.”); Parks, W. Hays, The International Law of Intelligence Collection, in National Security Law 433, 433–34 (Moore, John Norton, Tipson, Fredrick S. & Turner, Robert F., eds., 1st ed. 1990)Google Scholar (“No serious proposal ever has been made within the international community to prohibit intelligence collection as a violation of international law because of the tacit acknowledgement by nations that it is important to all, and practiced by each.”); Dermarest, Geoffrey, Espionage in International Law, 24 Denv. J. Int'l. L. & Pol'y 321, 321 (1996)Google Scholar (“International Law regarding peacetime espionage is virtually unstated, and thus international law has been an inappropriate and inadequate reference for either condemnation or justification of actions involving intelligence gathering.”); Baker, Christopher D., Tolerance of International Espionage: A Functional Approach, 19 Am. U. Int'l. L. Rev. 1091, 1091 (2004)Google Scholar (“Espionage is curiously ill-defined under international law, even though all developed nations, as well as many lesser-developed ones, conduct spying and eavesdropping operations against their neighbors.”); Silver, David, Intelligence and Counterintelligence, in National Security Law 935, 965 (Moore, John Norton & Turner, Robert F. eds., 2d ed. 2005)Google Scholar (“There is something almost oxymoronic about addressing the legality of espionage under international law … despite the ambiguous state of espionage under international law, it is not specifically prohibited by treaty or other international legal mechanism.”); Chesterman, Simon, The Spy Who Came in From the Cold War: Intelligence and International Law, 27 Mich. J. Int'l. L. 1071, 1072 (2006)Google Scholar (“Despite its relative importance in the conduct of international affairs, there are few treaties that deal with it directly. Academic literature typically omits the subject entirely, or includes a paragraph or two defining espionage and describing the unhappy fate of captured spies. For the most part, only special regimes such as the laws of war address intelligence explicitly. Beyond this, it looms large but almost silently in the legal regimes dealing with diplomatic protection and arms control.”); Smith, Jeffrey H., Keynote Address: State Intelligence Gathering and International Law, 28 Mich. J. Int'l L. 543, 544 (2007)Google Scholar (“Most lawyers would likely scoff at the notion that espionage activities are constrained in any meaningful way by international law. Indeed most probably believe that international law's only influence on espionage is that in wartime, spies caught behind the lines out of uniform can be shot. Hardly a sophisticated or, to intelligence services, comforting notion.”).

² Cooke, Peyton, Bringing the Spies in from the Cold: Legal Cosmopolitanism and Intelligence Under the Laws of War, 44 U. San Fran. L. Rev. 1, 9 (2010)Google Scholar (“Very little international law addresses intelligence. Indeed, beyond bilateral and multilateral intelligence-sharing treaties, which do not address intelligence methods, no in-depth treatment of intelligence exists in international law. While some bodies of international law, such as the law of war or human rights law, can potentially provide for substantial intelligence oversight, the international law of intelligence itself does not. Intelligence-as-intelligence occupies very murky place in international law that might be characterized as either legal but discouraged or illegal but not enforced. To the extent that international intelligence law exists, it does not provide an effective mechanism for intelligence regulation.”). Most recently, the international group of experts who worked at the invitation of the NATO CCDCOE concluded that espionage was not per se regulated under international law. Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations 168 (2d ed. 2017).

³ Sulmasy, Glenn & Yoo, John, Counterintuitive: Intelligence Operations and International Law, 28 Mich. J. Int'l L. 625, 637–38 (2006)Google Scholar (“International law has never prohibited intelligence collection, in peacetime or wartime… . The history of state practice reveals that the regulation of intelligence gathering has always been left to domestic enforcement… . Calls to pursue the establishment of international entities or international law to regulate the intelligence collection activities of nations-states are counterproductive.”).

⁴ Radsan, John, The Unresolved Equation of Espionage and International Law, 28 Mich. J. Int'l L. 595, 597 (2007)Google Scholar.

⁵ Falk, Richard A., Space Espionage and World Order: A Consideration of the Samos-Midas Program, in Essays on Espionage and international Law 45, 68 (Stranger, Roland J. ed., 1962)Google Scholar.

⁶ Chesterman, supra note 1, at 1072; Buchan, Russell, The International Legal Regulation of State-Sponsored Cyber Espionage, in International Cyber Norms: Legal, Policy and Industry Perspectives 84 (Osula, Anna-Maria & Rõigas, Henry eds., 2016)Google Scholar. Suggesting that all states spy but simultaneously all states also criminalize espionage when done unto them—thus state practice and opinio juris run in opposition.