The chapter outlines the distinct features and challenges of the legal regimes for the cooperation by states with international criminal jurisdictions. State compliance with the tribunals’ orders or requests for cooperation is key to their effective functioning absent direct law-enforcement and given the necessary reliance upon national authorities for executing arrests, obtaining evidence, enabling the collection of evidence, carrying out coercive measures, enforcing sentences, and so on. While being in theory more stringent than the ‘horizontal’ schemes for inter-state cooperation in criminal matters, the cooperation regime remains the Achilles heel of international criminal justice in the lack of failproof mechanisms for compelling compliance. The chapter sets out the scope, parameters, and addresses of the obligations to cooperate with UN ad hoc tribunals and the International Criminal Court; the extent to which such obligations can be allowed to prevail over conflicting duties; and the ability of parties in the proceedings to seek cooperation from the respective duty-bearers. It also discusses issues arising in connection with the cooperation for the arrest and surrender of suspects and related to other forms of assistance to international criminal jurisdictions, as well as the challenges of enforcing cooperation obligations and addressing non-compliance.

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.