This chapter discusses general principles of liability as they apply across the various offences and provide for the doctrines by which a person may commit, participate in, or otherwise be found responsible for those crimes. They include forms of liability such as aiding and abetting, which are familiar to all domestic criminal lawyers, as well as principles like command responsibility, which are specific to international criminal law.

This chapter describes: the creation of the ICC; its main features (such as its jurisdiction and its rules for selecting cases); opposition and criticisms; and a brief assessment of its work, including its controversial and sometimes disappointing early efforts, and the challenges that the Court confronts. The chapter discusses the Court’s jurisdiction – including personal and territorial jurisdiction, temporal jurisdiction, and subject matter jurisdiction. It discusses the ‘trigger mechanisms’: State Party referrals (including self-referrals), Security Council referrals, and initiation by the Prosecutor. It explains preliminary examination, investigation, and prosecution, as well as the selection criteria of admissibility (complementarity and gravity), and the interests of justice. It discusses opposition to the ICC, including the criticisms from the United States and the African Union, as well as key developments, such as US attacks on the ICC and threats of withdrawal from the African Union. The chapter reviews the Court’s record, including problems of collapsed cases, slow proceedings, the early focus on Africa, and accusations of selectivity and bias, as well as recent indications of progress.

This chapter discusses the principles of jurisdiction as they relate to international crimes. International law tends to allow jurisdiction over international crimes on broader bases than it offers over other crimes. Therefore, this chapter must be read with the caveat that it is not intended to be a general discussion of the international law of jurisdiction.

This chapter begins by discussing how the crime of aggression differs from all other core international crimes in being inextricably linked to an act of aggression by a state against another state. It then turns to a discussion of the history of the crime of aggression, including its inclusion in the Statute of the International Criminal Court (ICC). It covers the definition of the crime of aggression as set out in Article 8bis of the ICC Statute, as well as its relationship with other crimes. It also examines the material elements: (1) by a perpetrator in a leadership position in a state (2) who has participated (3) in an act of aggression by the state (4) which ‘by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations’. It also explains the mental elements as set out in Elements 4 and 6 of the ICC’s Elements of Crime; the jurisdiction of the ICC over aggression, including the role of the Security Council; and the implications of an ICC prosecution of the crime of aggression.

This chapter discusses defences, which are a fundamental part of criminal law, and reflect important limitations on the proper scope of punishable conduct. It is the purpose of this chapter to set out and critique the law relating to defences, in both treaty-based and customary international law. This chapter is concerned with substantive defences; it does not deal with issues such as immunity, youth, ne bis in idem, or limitation periods.

The chapter highlights the central role national jurisdictions (should) play in the system of international criminal enforcement and addresses the most common legal issues and practical obstacles which may obstruct the pursuit of accountability at the domestic level. The chapter provides an overview of the relevant state practice from the earlier notable precedents to the most recent instances of prosecution and adjudication of core crimes before domestic courts, in particular under the universal jurisdiction. It clarifies the scope of the duties international law imposes on states, including the obligation to extradite or prosecute. The chapter then zeroes in on every principal issue related to the domestic prosecution and adjudication of international crimes, such the need for adequate implementing legislation as well as the extent to which domestic prosecutions may be hindered by the statutes of limitations, the prohibition on retroactive application of penal provisions, and the principle of ne bis in idem (double jeopardy). The chapter’s final section addresses the political and practical obstacles to tackling impunity for international crimes at the domestic level.

In response to two conflicts in the 1990s - the Yugoslav wars of dissolution and the Rwandan genocide of 1994 - the United Nations (UN) UN Security Council created the International Criminal Tribunals for the Former Yugoslavia and Rwanda (ICTY and ICTR). This chapter begins with the creation of the ICTY through UN Security Council Resolution 827, the court’s three organ structure (Registry, Office of the Prosecutor, and Chambers), jurisdiction, and relationship with national courts. The chapter examines the milestones of the ICTY, from its first case through to the conflict in Kosovo, prosecution of former Heads of States, and implementation of its Completion Strategy, and assesses the critiques of the tribunal. The chapter then turns to the history of the creation of the ICTR, its structure (which was similar to that of the ICTY), and its jurisdiction. It then examines the practice of the ICTR, from its initial troubles through the prosecution of the leaders of the genocide, and the implementation of its Completion Strategy. Both Tribunals have now closed and transitioned into a residual phase.

This chapter provides an overview of responses to situations of mass atrocity and armed conflict outside of criminal prosecution. The chapter begins by discussing transitional justice. It then turns to a description and analysis of specific forms of transitional justice: amnesties, truth and reconciliation commissions, lustration, reparations and civil claims, and local justice mechanisms. It defines each of these terms and discusses their international law status, positive and negative features, and, where applicable, the relationship of that form of transitional justice to the International Criminal Court, and use in domestic systems. This chapter provides examples of each form of transitional justice, such as amnesties implemented in Latin American countries, the South African Truth and Reconciliation Commission, lustration in Eastern Europe after the end of communism, reparations in Germany after World War II, and local justice mechanisms in northern Uganda.

This chapter begins with the history of the international recognition of terrorism as a crime, including through the adoption of global and regional counter-terrorism treaties, and United Nations (UN) Security Council resolutions. The chapter then turns to a discussion of the challenges associated with defining terrorism, including its material and mental elements, and with national prosecutions. The chapter also explores terrorism as a war crime, a crime against humanity, and a crime under customary international law. The chapter’s consideration of torture begins with the definition found in the UN Convention Against Torture, and considers the obligation to prosecute or extradite (aut dedere aut judicare) under that treaty. It also discusses torture as an international crime under the ICC Statute and other statutes of international criminal tribunals. The chapter ends with an examination of ecocide as an emerging crime.

This chapter discusses international criminal law (ICL) and distinguishes it from other areas of international law and criminal law. ICL is placed within the general area of international alw and its source doctrine whilst also discussing ICL’s unique nature as an area of criminal law. Critical approaches to ICL are discussed as an increasingly important perspective/approach to shaping debates in ICL.

This chapter introduces some of the justifications for punishment and the purposes it seeks to achieve. It will also consider the wider goals which are claimed for international criminal law, alongside some of the challenges to international criminal law that have arisen.

The chapter explains the principles of inter-state cooperation in criminal matters in connection with domestic proceedings. It sets out the international legal framework governing criminal law cooperation among states, including multilateral and bilateral agreements of general application and treaties specifically concerning international crimes, most notably the 2023 Ljubljana–The Hague Convention on International Cooperation in the Investigation and Prosecution of the Crime of Genocide, Crimes Against Humanity and War Crimes. The chapter sets out the differences between the traditional forms of assistance in criminal matters, which are associated with a higher degree of formality and subject to broader grounds for refusal and, on the other hand, the more advanced forms of cooperation (exemplified by mutual recognition in the European Union context) prioritizing effective enforcement while recognizing limited grounds to refuse requests. The chapter reviews the prerogatives of the requested states to refuse under these models with reference to double criminality, specialty, statutory limitations, ne bis in idem, and human rights concerns. It then takes a closer look at the traditional forms of cooperation and the issues which arise in that context, focusing on extradition, other mutual legal assistance, transfer of criminal proceedings, and enforcement of foreign penalties.

The chapter addresses the penal regime of international criminal jurisdictions, focusing primarily on the law and practice of the UN ad hoc tribunals and the International Criminal Court (ICC). It sets out the categories of penalties which may be imposed by international criminal courts and tribunals for the core crimes and the offences against the administration of justice. The chapter sets out the commonly-adduced general purposes for punishing perpetrators of international crimes (retribution, deterrence, rehabilitation, etc.) and addresses the extent to which the punishment rationales acknowledged at the national level remain valid within the international penal regime. It analyses the international jurisdictions’ sentencing principles and practice, in particular the need for the individualization of penalties while ensuring consistency in sentencing and the relative weight accorded to aggravating and mitigating circumstances in determining the appropriate sentence. The chapter also surveys the procedures at sentencing, in particular the option of following the unified or bifurcated process for the determination of the guilt or innocence and, if appropriate, the sentence, as well as the arrangements adopted for pardon, early release (commutation) and review of sentences.

This chapter discusses the immunities of individuals in relation to criminal prosecution for international crimes. It introduces the main two types of immunity: functional immunity and personal immunity. It discusses diplomatic immunity as a particular illustration. The chapter then discusses limits on functional immunity, with the Pinochet decision and other precedents. It then discusses the harder situation of personal immunity, as explained by the International Court of Justice in the Arrest Warrant Decision. It reviews various ways that states have relinquished immunity, including through Security Council resolutions under Chapter VII of the UN Charter, or through ratification of the ICC Statute. The chapter surveys the many issues about whether Security Council referrals to the ICC, coupled with a duty to cooperate fully, have the same effect of removing immunity. The chapter then discusses the legal position advanced by the Sierra Leone Special Court in the Taylor case, and endorsed by the ICC Appeals Chamber in the Al Bashir case, that there are no immunities before international courts, by virtue of their special nature. The chapter canvasses criticism of the theory as well arguments in favour of it.