Customary International Law Resources


I. General Background on Customary International Law

II. Domestic Interaction with International Law

III. Principle of Legality

IV. Sentencing

V. Cases from Other Jurisdictions

VI. Additional Materials



I. General Background on Customary International Law


 Crawford, Part I Preliminary Topics, in  The Sources of International Law, Brownlie’s Principles of Public International Law (8th Ed., Oxford Public International Law, 2012) [unavailable online without purchase]

  • Details the sources of international law – treaties, custom, general principles, judicial decisions, and subsidiary sources. Explains the elements of custom and reviews foundational cases.


Schlutter, Developments in Customary International Law (2010) [unavailable online without purchase]

  • Provides an overview of the current status of customary international law. Includes a comprehensive synopsis of the current literature and contrasts the practice of the ICTY/ICTR with jurisprudence of the International Court of Justice.


Mendelson, The Formation of Customary International Law (1998) [available online with subscription]

  • Detailed overview of customary international law elements and identification. Explores the creation of new principles of customary international law. Details the benefits and challenges in utilizing customary international law.



Meron, Revival of Customary Humanitarian Law, Am.J.Int’l.L (2005) [available online with subscription]

  • The author asserts that at least in the field of humanitarian law, customary law continues to thrive and to depend in significant measure on the traditional assessment of both state practice and opinio juris. In particular, this essay explores the ways that the nullum crimen sine lege principle has affected the application of customary humanitarian law by the criminal tribunals.


Mettraux, Crimes Against Humanity in the Jurisprudence of the ICTY and ICTR, Harv Int’l L.J. (2002) [available online with subscription]

  • This article analyzes how the International Criminal Tribunal for the former Yugoslavia (ICTY) and the International Criminal Tribunal for Rwanda (ICTR) have played a crucial role in the transformation of crimes against humanity into an international offense.


Scharf, Accelerated Formation of Customary International Law, ILSA J. of Int. & Comparative Law (2014) [available for free online]

  • This article examines the phenomenon of accelerated formation of customary international law. It argues that in periods of fundamental change, whether by technological advances, the commission of new forms of crimes against humanity, or the development of new means of warfare or terrorism, customary international law may form much more rapidly and with less state practice than is normally the case to keep up with the pace of developments.



International Court of Justice, North Sea Continental Shelf Cases (1969) [available for free online]

  • The foundational International Court of Justice decision which lays out customary international law’s dual requirements of state practice and opinio juris. Highlights the issue of “specially affected” states and dispels the notion that duration of practice is a necessary element of customary international law.


II. Domestic Interaction with International Law


Björgvinsson, The Intersection of International Law and Domestic Law (2016) [available online with subscription]

  • Investigates the theoretical and practical issues relating to the intersection between domestic and international law. Discusses theories of monism and dualism, the rules relating to treaty making and their ratification, the doctrine of automatic incorporation and transformation, the direct effect of international norms in the domestic system, and the principle of consistent interpretation.


Crawford, Part I Preliminary Topics, 3. The Relations of International and National Law, in Brownlie’s Principles of Public International Law (8th Ed., Oxford Public International Law, 2012) [unavailable online without purchase]

  • Succinct overview of the relationship of international and national law and the issues that arise at that nexus.


Ferdinandusse, Direct Application of International Criminal Law in National Courts (2006) [unavailable online without purchase]

  • The author examines the concept of the direct application of international criminal law in national courts. He provides a description of the relevant practice in different states ranging from Argentina to Senegal and their prosecution of crimes like genocide, crimes against humanity, and war crimes.


Killander & Adjolohoun, International law and domestic human rights litigation in Africa (2010)  [available for free online]

  • This book challenges the traditional monist-dualist dichotomy by exploring international human rights practice in African domestic courts. Examines how domestic courts in Africa have used international human rights law to interpret and fill gaps in national laws.


Nijman & Nollkaemper, New Perspectives on the Divide Between National and International Law (2007) [available online with subscription]

  • This book contributes to the understanding of one of the most pressing issues of modern international law: the relationship between the international legal order and the domestic legal orders of sovereign states. Chapters cover topics such as: domestic implementation of international law, monism/dualism, the globalization of state constitutions, and the emerging universal legal system.


Novakovic, Basics Concepts of public International Law: Monism and Dualism (2013) [unavailable online without purchase]

  • Articles written by fifty-five authors from thirty-two countries on monism and dualism in various countries and contexts.



Borchard, Relation Between International Law and Municipal Law, VA Law Review (1940) [available for free online]

  • Written in 1940, this article provides an analysis of the approach taken by the two major schools of thought regarding the relationship between international law and municipal law: monism and dualism.


Ginsburg, Locking in Democracy: Constitutions Commitment and IL, NYU Journal of IL (2006) [available for free online]

  • This article looks at the effects of international law on domestic governance as well as the effects of domestic institutions on international cooperation by treating international commitment as a function of domestic constitutional design. It finds that new democracies tend to be more open to customary international law and to provide for treaty-making structures that build on the logic of precommitment.


Klein, A Theory for the Application of the Customary International Law of Human Rights by Domestic Courts, Yale Journal of IL (1998) [available for free online]

  • This Comment emphasizes the common law nature of international legal principles, and distinguishes them from positive rules articulated in treaties. It argues that these principles derive their self-executing character from the universal recognition of the rights they articulate, and not merely from domestic statutes purporting to execute them.


Nollkaemper, Internationally Wrongful Acts in Domestic Courts, A. J. Int’l L. (2007) [available for free online]

  • Principles of international responsibility provide guidance to the consequences that domestic courts should attach to a finding that the forum state has acted or is about to act in breach of its international obligations, for instance in cases such as Sanchez-Llamas and Medellin. This article explores the situations in which principles of international responsibility indeed may be relevant to domestic courts and discusses the normative foundation of their application at the domestic level. It also explains how domestic courts can contribute to the implementation of international responsibility.


Nollkaemper, The Duality of Direct Effect of International Law, Euro J. Int’l L. (2014) [available for free online]

  • This article assesses how, fifty years after the European Court of Justice delivered its judgment in Van Gend en Loos (VGL), the doctrine of direct effect of international law has fared outside the European Union.


Roht-Arriaza, Just a ‘Bubble’? Perspectives on the Enforcement of ICL by National Courts (2013) [available for free online]

  • This article examines the forward movement and the backlash of the enforcement of international criminal law by national courts, drawing in particular on the Latin American and the Spanish examples. It concludes by arguing that the hangover after the euphoria should be used to correct the sky-high expectations and to (re)determine the relationship between international and national and among different national jurisdictions.


Sloss & Van Alstine, International Law in Domestic Courts (2015) [available for free online]

  • Analyzes the role of domestic courts in the creation, interpretation, recognition, implementation, and modification of international norms in domestic courts. Recognizing that beyond “stages of governance,” a decisive factor in explaining the engagement of domestic courts with international law is the nature of the legal rule at issue.


Waters, Creeping Monism, Columbia Law Review (2007) [available for free online]

  • This Article offers a narrow lens analysis of a key debate over the role of foreign authority in U.S. courts: the use of international human rights treaties in interpreting domestic law. Drawing on a six-year study of judicial treatment of the International Covenant on Civil and Political Rights by the U.S. Supreme Court and four other common law jurisdictions, the Article develops a typology of interpretive incorporation techniques that courts are utilizing. It also provides statistical evidence regarding the use of human rights treaties across jurisdictions. Finally, it maps out a possible normative framework for evaluating courts’ use of human rights treaties in interpreting domestic law.


Wildhaber, Relationship btwn CIL and Municipal law in Western. Euro Countries, Max-Planck (1988) [available for free online]

  • This article concentrates on an examination of civil law jurisdictions, that make reference to public international law in their constitutions as being an integral part of its laws, and whether they indeed give priority to general international law requirements, even when faced with statutes-and decrees that appear clearly to violate them.



Deschnes Commission (Canada), Commission of Inquiry on War Criminals (1986) [available for free online]

  • Discussion of the direct application of customary international law, finding that customary international law is adopted lato sensu into Canadian law and can form the basis of criminal prosecution in Canada when there is no domestic law to the contrary.


III. Principle of Legality



Cassese, “The Principle of Legality” in International Criminal Law (3rd Ed., 2013) [draft version of chapter available for free online]

  • Cassese’s foundational text covers the main substantive and procedural aspects of international criminal law. The chapter on the “Principle of Legality” describes the principle and distinguishes varying articulations.


Gallant, The Principle of Legality in International and Comparative Criminal Law, Cambridge Studies in International and Comparative Law (2009) [available for free online]

  • Study of the status of legality in international law – in international criminal law, international human rights law, and international humanitarian law. Survey on legality/non-retroactivity in national constitutions and the principle of legality in various legal systems around the world.



Dana, Beyond Retroactivity to Realizing Justice: A Theory on the Principle of Legality in ICL Sentencing (2009) [available for free online]

  • This article seeks to develop the normative content of nulla poena sine lege (no punishment without law) under international law and critically evaluate the statutes of international criminal courts and their sentencing jurisprudence on genocide, crimes against humanity, and war crimes. The author argues for an understanding of nulla poena that it is not merely a protection against retroactive punishment, but is crucial to international criminal justice principles such as equality before the law, consistency in punishment, and legitimacy in international prosecutions.


Namwase, The Principle of Legality and the Prosecution of International Crimes in Domestic Courts (2011) [available for free online]

  • This study seeks to contextualise the discourse surrounding the principle of legality and the domestic prosecution of international crimes in Africa, focusing on the domestication of the Rome Statute in Uganda and the decision to prosecute domestically a former commander of the Lord’s Resistance Army. Ultimately, the paper finds that the principle of legality does not and should not bar prosecution of international crimes in Africa.


Van Schaack, Crimen Sine Lege: Judicial Lawmaking at the Intersection of Law and Morals, Georgetown Law Journal (2008) [available for free online]

  • This article notes that even where new standards have been applied to past conduct, these cases have not infringed on the principle of legality because today’s defendants were on sufficient notice of the foreseeability of ICL jurisprudential innovations in light of domestic penal law, universal moral values in international human rights law, developments in international humanitarian law, etc. The article argues that any lingering concerns about the rights of the defendants can and should be mitigated by sentencing practices that are closely tethered to extant domestic sentencing rules governing analogous domestic crimes.


Van Schaack, The Principle of Legality in International Criminal Law, ASIL Proceedings (2010) [available for free online]

  • In panel remarks, this professor discusses how ICL tribunals are applying new norms to past conduct and thus are engaged in a refashioning of ICL. However, this does not compromise the fundamental fairness of modern ICL proceedings because the jurisprudence is largely consistent with the international formulations of the principle of legality, authoritative interpretations emerging from institutions charged with enforcing human rights protections, and the purposes underlying the principles of nullum crimen sine lege.


IV. Sentencing



Robert Cryer, et al., Introduction to International Criminal Procedure (2007) [unavailable online without purchase]

  • Basic overview on guilty pleas and plea bargaining in international tribunals as well sentencing and penalties. Details the purposes of sentencing and its practice at the international tribunals. See Chapter 17, pg. 467: Admission of guilt, guilty pleas, plea bargaining; Chapter 19, pg. 494: Sentencing and Penalties (additional resources listed on pg. 505-506).


Frederik Harhoff, Chapter 9: Sense and Sensibility in Sentencing, Taking Stock of International Criminal Punishment 133-152 (2007), in Law at War: The Law as it Was and the Law as it Should Be (2008) [available online with subscription]

  • This chapter offers a few observations on international sentencing based respectively upon the practice of the two UN Criminal Tribunals for the Former Yugoslavia (ICTY) and Rwanda (ICTR). The sentencing principles developed so far by the Tribunals in respect of war crimes are of course derived from the principles in domestic law. The chapter also takes a closer look at the judicial process whereby sentences are determined under international criminal law by international criminal tribunals that are competent to prosecute individuals for genocide, crimes against humanity and war crimes.


Daniel B. Pickard, Proposed Sentencing Guidelines for the International Criminal Court (1997) [available online for free]

  • General background on sentencing in international tribunals and review of historical sentencing principles. Presents analytical model detailing proposed sentencing guidelines for international crimes of genocide, crimes against humanity, and war crimes.


Andrew N. Keller, Punishment for VIolations of International Criminal Law; An Analysis of Sentencing at the ICTY and ICTR (2001) [available online for free]

  • Review of sentencing issues at the ICTY and ICTR. Background on the relevant statutory provisions in the ICTR/ICTY regarding sentencing and philosophy of sentencing. References specific cases in these tribunals.


Barbara Hola, Sentencing of International Crimes at the ICTY and ICTR: Consistency of Sentencing Case Law (2012) [download for free]

  • This article analyses ‘consistency in approach’ of sentencing ICTY and ICTR. The conclusions demonstrate that on a general level, a set of sentencing principles is consistently emphasized in the ICTY and ICTR cases. The inconsistencies and disparities across cases are, however, identified with respect to particularities, such as what factors are relevant for the gravity assessment and whether a particular mitigating/aggravating factor indeed aggravates/mitigates the sentence in a particular case. On the basis of a critical examination of the ICTY and ICTR case law the article offers suggestions on how to develop more transparent and understandable sentencing practices.


William A. Schabas, Sentencing by International Tribunals: A Human Rights Approach (1997) [available online for free]

  • This article addresses issues raised in sentencing offenders before the ICTY and ICTR. In particular, it argues that there needs to be greater attention paid to the nexus of international criminal and human rights law.


V. Cases from Other Jurisdictions


Argentina, Priebke (1995) [available for free online, in Spanish only]

  • In a case about the extradition of a German officer charged with genocide and other war crimes/crimes against humanity, the Supreme Court found customary international law to be directly applicable in the domestic legal order.


Australia, Nulyarimma v Thompson (1999) [available for free online]

  • In this case, concerning the treatment of aboriginals in Australia, the Federal Court held that the international crime of genocide could not be prosecuted under Australian law without implementing legislation.


Botswana, Republic of Angola v Springbok Investments (2005) [available for free online]

  • The High Court concluded that the rules of international law form part of the law of Botswana, as a “member of the wider family of nations,” unless they conflict with national legislation or common law.


Canada, R. v. Hape (2007) [available for free online]

  • R v Hape is a case on appeal to the Supreme Court of Canada regarding a cross-border crime. The court found customary international law to be applicable in Canada stating para. 39 “following the common law tradition, it appears that the doctrine of adoption operates in Canada such that prohibitive rules of customary international law should be incorporated into domestic law in the absence of conflicting legislation. The automatic incorporation of such rules is justified on the basis that international custom, as the law of nations, is also the law of Canada unless, in a valid exercise of its sovereignty, Canada declares that its law is to the contrary.”


Canada, Bouzari v Iran (2004) [available for free online]

  • The Court of Appeal for Ontario citing the doctrine of adoption at para. 65 stating: “…customary rules of international law are directly incorporated into Canadian domestic law unless explicitly ousted by contrary legislation”.


Canada, R v Finta (1994) [available for free online]

  • In the 1994 case v. Finta, Imre Finta, a Canadian citizen, that was originally a Hungarian national, was brought before the Toronto court to stand trial for eight counts of war crimes and crimes against humanity. On addressing claims raised in cross appeal the Supreme Court addressed whether the impugned sections of the Canadian criminal code violated the Canadian Charter of Rights and Freedoms by reason of vagueness. The court found that it did not violate the Charter, stating “Section 11(g) of the Canadian Charter allows customary international law to form a basis for the prosecution of war criminals who have violated general principles of law recognized by the community of nations regardless of when or where the criminal act or omission took place.” Cory J., para 64.


England, Trendtext Trading Corporation Ltd v. Central Bank of Nigeria (1977) [available for free online]

  • The Court of Appeal established that the rules of international law formed part of English law, explaining that the doctrine of incorporation better incorporates the inevitable changes in the rules of international law.


England, R v. Jones (2006) [available for free online]

  • The House of Lords rejected the idea that new crimes under international customary law automatically become crimes under domestic law. However, the court stated that it would be “at least arguable that war crimes, recognised as such in customary international law, would now be triable and punishable under the domestic criminal law of this country irrespective of any domestic statute.” The court did not conclusively answer this question in the case as it determined it was not at issue (distinguishing the crime of aggression from war crimes).


Hungary, Decision 53/1993 [available for free online]

  • The Constitutional Court was requested by the President to review the constitutionality and the compatibility with international law of a law enacted by Parliament in order to extend the non­-applicability of statutory limitations to offences committed during the 1956 events. The Court addressed, in turn, the relationship between international law and the domestic law of Hungary, the relationship between international criminal law and national criminal law in general, and the non­-applicability of statutory limitations to international crimes under customary and treaty law.


India, Gramophone Company Of India Ltd vs Birendra Bahadur Pandey & Ors (1984) [available for free online]

  • The Supreme Court found that although treaties are considered to be non self-executing and thus formal adoption into domestic law is required, “rules of customary international law that are not contrary to the municipal law are deemed to be incorporated in the domestic law.”


Kenya, Rono v Rono (2005) [available for free online]

  • The Court of Appeal found that courts could apply customary international law, even in the absence of implementing legislation as long as it did not conflict with domestic law. The court stated, “[T]he current thinking on the common law theory is that both international customary law and treaty law can be applied by State Courts where there is no conflict with existing state law, even in the absence of implementing legislation.”


Netherlands, re Nyugat (1959) [unavailable online without purchase]

  • In re Nyugat the Supreme Court found that Article 66 (now Article 94) of the Netherlands Constitution granted the Court authority to review domestic law for compatibility with international law, limited to self-executing provisions of treaties and decisions of international institutions.The court precluded the application of customary international law on prize. During Constitutional revision in 1983 the Government upheld the Supreme Court’s narrow doctrine meaning that matters of customary law remain outside the courts’ reviewing mandate.


 VI. Additional Materials



Carter, Ellis, & Jalloh, The International Criminal Court in an Effective Global Justice System (2016) [available online with subscription]

  • This book analyzes the interactions of international criminal tribunals established since the 1990s with international, national and regional bodies, making recommendations for the International Criminal Court (ICC) as it goes forward. Placing the core issues within the statutory framework of the Rome Statute and major policy considerations, the authors examine ways in which the ICC can best coordinate with other accountability mechanisms on national and regional prosecutions, the UN Security Council, cooperation on the enforcement of arrest warrants, national non-judicial processes and amicus briefs from non-governmental organizations (NGOs).


Du Plessis, African Guide to International Criminal Justice (2008) [available for free online]

  • The African Guide to International Criminal Justice provides a comprehensive and accessible introduction for government legal and judicial officers, the police and practising lawyers in African states to the subject of international criminal law and recent developments in the field.


Cherif Bassiouni, Introduction to International Criminal Law (2003) [unavailable online without purchase]

  • This textbook covers the history, nature, and sources of international criminal law; the ratione personae; ratione materiae–sources of substantive international criminal law; the indirect enforcement system; the direct enforcement system; the function of the international criminal court; rules of procedure and evidence applicable to international criminal proceedings; and the future of international criminal law.


Sellers & Tomaszewski, The Rule of Law in Comparative Perspective, Jus Gentium: Comparative Perspectives on Law and Justice (2010) [unavailable online without purchase; however, much of the book is viewable online for free on Google books]

  • This text compares the different conceptions of the rule of law that have developed in different legal cultures. Lawyers and legal scholars from various legal systems describe the social purposes and practical applications of the rule of law, and how it might be improved in the varied circumstances of their own courts and politics.