At first blush, “comparative international law” might sound like an oxymoron. In principle, international law—at least when it arises from multilateral treaties or general custom—applies equally to all parties or states. As a result, international lawyers often resist emphasizing local, national, or regional approaches due to the field’s aspirations to universality and uniformity. Comparativists, meanwhile, frequently overlook the potential to apply comparative law insights to international law on the basis that “rules which are avowedly universal in character do not lend themselves to comparison.”

To develop international law claims, it is often critical to compare different countries’ laws. This essay explores how methods drawn from comparative law and comparative politics research can help international lawyers make comparative inquiries more simply and straightforwardly.

International lawyers recognize three main sources of legal authority: treaties, custom, and general principles. Cross-national comparisons are deeply embedded in the very definitions of two of these three sources. To establish international custom, an international lawyer must show that a broad range of states consistently engage in a certain practice out of a sense of legal obligation. To establish a general principle, an international lawyer must show that it is “recognized by civilized nations”; in practice this requires that the principle be found in diverse legal families. Treaty interpretation does not necessitate cross-country comparison as a matter of definition: in theory, the text of the treaty itself could provide the requisite answers. However, in practice, international and domestic courts are typically faced with ambiguous treaty terms. To interpret them, they often turn to the jurisprudence of diverse states and to subsequent state practice, thus implicitly beginning a comparative inquiry. in sum, comparative international law is useful for identifying and applying international law, as this volume’s introduction explains.

For a significant period of time, the comparativist and the international lawyer were considered to inhabit different worlds: the former scrutinized similarities and differences between domestic legal systems while the latter focused on the universal realm of international law that overlays these systems. This comfortably segregated image has been conclusively shattered by numerous studies demonstrating the multiple areas of interaction between international and comparative law. of these, one of the ripest areas for further reflection is the “general principles of law” as a source of international law. Puzzlingly, given the traditional domestic law origins of the general principles of law, comparative law and methodology have rarely featured in the scholarship and jurisprudence on the general principles. Thus, the attempt of the International Criminal Tribunal for the Former Yugoslavia (Icty) to use the general principles as a freestanding source of international criminal law provides a particularly intriguing opportunity to study the interaction between international and comparative law.

Public international law and comparative law have so far been regarded as largely distinct fields, with little to no overlap between them. The degree of separation between the two disciplines is rendered in particularly stark relief by the absence in practice or scholarship of any real inquiry into the relationship between comparative law on the one hand and customary international law and general principles of international law on the other. Some eminent international lawyers go so far as to claim that it would be both unnecessary and unrealistic to have recourse to comparative law in the context of the identification of customary international law and general principles of law, pointing to the case law of the Permanent Court of International Justice and the International Court of Justice, which, according to them, “show[s] a clear disinclination towards the use of the comparative method.”

International legal scholars have long recognized the importance of the rules and processes by which states adhere to international legal obligations and “translate” them into their domestic legal systems. Research by political scientists on specific issue areas likewise increasingly recognizes that domestic implementation is crucial to international law compliance and effectiveness. Yet the lack of systematic data makes it difficult to assemble an overall picture of the relationship between international law and domestic law around the world, let alone to document its evolution over time. Recent qualitative surveys of state practice have begun to fill that gap, but provide only a snapshot in time and are limited to relatively few countries. Some quantitative projects cover more countries, but address only a limited number of questions based solely on the text of national constitutions.

Comparative international law promises to bring fresh attention to the similarities and differences in how international law is understood and approached at the domestic level. Comparative international human rights law applies this focus to similarities and differences in the ways that international human rights law is, for example, interpreted at the domestic level by courts.

Historical practice, or custom, has long been seen as a source of authority in the resolution of separation-of-powers disputes. In two recent cases assessing the limits to the president’s power regarding the recognition of foreign nations and the making of recess appointments, the Supreme Court heavily emphasized past practice. Historical practice, the Court said, reflects “the compromises and working arrangementsth at the elected branches of Government themselves have reached.” in the realm of war powers, the executive branch has long relied on custom to justify military initiatives that were carried out without congressional approval. In essence, the executive has argued that because force has been used in the past without congressional approval, the same is permissible in various other situations (for example, in the Dominican Republic, Grenada, Haiti, Kosovo, and Panama).

In their eagerness to justify the “United States perspective” on the Kampala definition of the crime of aggression and on the International Criminal Court (ICC), Koh and Buchwald tend to invent imaginary enemies and to ascribe to them views that they do not actually hold. In so doing, the authors weaken a thesis that, in some respects, is not devoid of interest. From at least two points of view, however, their article is paradoxical, if not pathetic—exactly like the U.S. position.

The fallout from the 2010 Kampala Review Conference for the United States has been explained by Harold Koh and Todd Buchwald, who were officially involved in the negotiations at the conference. The concerns they enumerate serve to implicate, inter alia, two issues of broad importance for the international community: the definition of the crime of aggression, and the clear divide between the positions of the permanent members of the UN Security Council and the rest of the Kampala participants with respect to the Councils role in implementing the Rome Statute’s new provisions on the crime of aggression. This Note, which focuses on those two issues, is partly a response to some of their criticisms and partly an independent assessment of the consequences of the Review Conference. It also evaluates the Kampala amendments to the Rome Statute’in particular, Articles 8 bis, 15 bis, and 15 ter—from the perspective of customary law and considers their impact on the role assigned to the Council under the UN Charter.

The three disparate cases decided by the International Court of Justice (Court or ICJ) in 2014 may not contribute much to the development of substantive international law, but they are instructive about the operations of the Court. Perhaps the Court was not at its finest in terms of coherent legal reasoning in these three cases; it certainly avoided difficult questions in all of them. Yet each of the three cases had significant numbers of separate and dissenting opinions, which sometimes reveal more about the Court’s reasoning than is apparent from the judgment or order itself.

On October 9, 2014, the Appeals Chamber of the International Criminal Court (ICC or Court) unanimously held that, under the ICC Statute, a trial chamber has the power to order witnesses to appear before it to give testimony in pending proceedings, which imposes legal obligations on the individuals concerned to comply. In so ruling, the appellate chamber upheld a controversial trial chamber decision granting the ICC prosecutor’s request to summon eight witnesses to testify in the joint trial of Kenya’s vice president, William Samoei Ruto, and former journalist Joshua arap Sang, both of whom faced charges of crimes against humanity for their alleged role in “post-election violence” that led to the deaths of over twelve hundred people (para. 9).

In a proceeding brought against the People’s Republic of China by the United States (in which Japan and the European Union joined), the Appellate Body of the World Trade Organization (WTO) ruled that China violated its obligations under the General Agreement on Tariffs and Trade 1994 (GATT)1 by imposing export restrictions on “rare earths,” minerals used in mobile phones, hybrid cars, and other high-tech products. In upholding the earlier decision of a WTO dispute settlement panel, the Appellate Body rejected China’s argument that export duties, quotas, and other restrictions could be justified by health and environmental concerns.

In Shepherd v. Germany, the Court of Justice of the European Union (ECJ) issued a preliminary ruling requested by a German administrative court in an asylum case brought by a United States Army service member. Applying the relevant asylum law of the European Union (EU), the ECJ held that, under certain circumstances, a conscientious objector who has deserted from his military unit may claim international refugee protection. It also clarified the conditions under which the basically legitimate prosecution of military deserters must be qualified as illegitimate persecution under international refugee law.

In only its second merits judgment, the African Court on Human and Peoples’ Rights (Court) placed strict limits on penalizing expression, especially that of journalists, in states party to the African Charter on Human and Peoples Rights (African Charter). In doing so, the African Court narrowly interpreted the often-criticized “clawback clauses” in the African Charter and relied instead on the tests of necessity, proportionality, and legitimate aim applied by other human rights tribunals to determine the legality of restrictions on rights.

In Zivotofsky v. Kerry, decided June 8, 2015, the United States Supreme Court (Court) held unconstitutional a federal statute that permitted U.S. citizens born in Jerusalem to designate “Israel” as their place of birth on their passports, notwithstanding the secretary of state’s decision that such passports should designate “Jerusalem” as the place of birth. The opinion resolved a relatively narrow question of law (the constitutionality of an unusual statute), but the justices’ reasoning and language are of potentially broad significance and will provide fodder for many doctrinal debates in U.S. foreign relations law.