How the law defines and protects all those persons who are not designated as combatants or POWs – civilians – forms the focus of Chapter 6. It examines how the law protects civilians generally in armed conflict, and in particular ‘protected persons’ – those who find themselves in the hands of an adverse power as enemy aliens or in situations of belligerent occupation. Chapter 6 examines the rules that Occupying Powers must observe when, in international armed conflicts, they find themselves in temporary possession of territory that belongs to another sovereign State. The phenomenon of long-term occupation is also examined, as is the law regulating the treatment of civilians in non-international armed conflict.

Chapter 8 looks at the general rules which apply to the means and methods of warfare, and what kinds of weapons have been prohibited or restricted under IHL. The general principles governing how warfare is conducted are explained – the prohibitions on causing unnecessary suffering and superfluous injury, and on indiscriminate means and methods. The chapter examines a number of particular weapons, such as dum-dum bullets, mines and booby-traps, weapons that leave non-detectable fragments in the human body, incendiary weapons, blinding laser weapons, cluster munitions and chemical and biological weapons. Chapter 8 also looks at the problem of explosive remnants of war being left in the conflict zone, as well as a number of means and methods which have been the focus of much attention but whose legality is highly contested, including nuclear weapons, white phosphorus, depleted uranium munitions, cyberwarfare, drone warfare and targeted killings. The chapter also explains prohibited methods of warfare such as ordering ‘no quarter’, perfidy, siege and pillage, along with the particular rules relating to belligerent reprisals, mercenaries, espionage and autonomous weapons.

The final substantive chapter of the book looks at how all these rules are implemented and enforced, and what mechanisms exist to hold violators of the law accountable for their acts. Common Article 1 of the Geneva Conventions requires states to ‘ensure respect’ for the rules of IHL, which is achieved through a range of measures such as education of the armed forces and civil society in the rules of IHL and entrenching the rules in domestic legislation. The chapter describes the roles of the ICRC, Protecting Powers and the International Humanitarian Fact-Finding Commission. The development and content of international criminal law are examined, including individual responsibility for war crimes, lesser violations of IHL, crimes against humanity and genocide, and the concept of command responsibility is explained. The growth in international and hybrid criminal tribunals is noted, as well as the roles played by the United Nations and other organisations in encouraging adherence to the rules of IHL. Finally the chapter examines mechanisms for implementation, enforcement and accountability in non-international armed conflict.

Chapter 1 looks at the historical development of IHL, from its origins in Europe in the 1850s, and the historical events that have shaped the law through the last century and a half. It describes the effect of the Battle of Solferino in 1861 on Henri Dunant, leading to the founding of the International Committee of the Red Cross in Geneva, as well as the parallel development of the Lieber Code arising out of the American Civil War. The core treaties and other instruments forming the basis of modern IHL are outlined, from the 1864 Geneva Convention to the more recent development of international criminal law and its contribution to the law of armed conflict

Chapter 9 examines the relationship between IHL and international human rights law (IHRL). Both bodies of law are concerned with protection of the human person, but there are some stark differences between the two. First, many IHRL instruments permit parties to derogate from their IHRL obligations in times of public emergency such as armed conflict, while IHL applies precisely at such times and permits of no derogation. Second is the difference in scope. IHL applies to all territory where an armed conflict is taking place, whereas IHRL has only limited extraterritorial application. This can lead to a direct conflict for a State, such as in a situation of occupation: the local law might violate IHRL obligations, yet under IHL the Occupying Power is required to respect that local law. Third, where IHL applies to both States and non-State actors, IHLR is primarily addressed to the State. In cases of overlap, harmony is preferred – both bodies of law apply. Where that is not possible because the conflict is direct, there are different views on how such conflicts should be reconciled. One view is that IHL, as the lex specialis, should prevail; the other is that the lex specialis doctrine will not always be appropriate. The conclusion is that although IHL and IHRL are slowly converging over time, there will still be situations where the differences are irreconcilable.

Chapter 7 looks at the law of targeting, which, in addition to imposing conditions on all targeting decisions, provides additional rules on the protection of civilians from the deleterious effects of armed conflict. The philosophical underpinnings of the law are explained, along with the core requirements of what constitute military objects and military objectives. Additional qualifications on permissible targeting are outlined – the requirements of proportionality and the precautions to be taken in attack, and the prohibition on indiscriminate attacks. The chapter explains the specific rules on targeting certain objects such as cultural property, the environment, medical facilities, works containing dangerous forces, objects necessary fo the survival or the civilian population and non-defended localities. The problem of dual-use (military/civilian) objects is examined, as is the law of targeting applicable in non-international armed conflict.

The Conclusions reflect on the law outlined in Chapters 1−10. They recall that IHL is essentially an attempt to balance two fundamentally contradictory drivers – the need to wage war effectively, and the need to protect people and property from the excessive effects of warfare. It concludes that IHL largely succeeds in this endeavour, and that without IHL life for those caught up in armed conflict would be immeasurably worse. It notes, however, that while the fundamental principles of IHL are enduring, States can and should do more to develop new or more comprehensive laws where there is a need, such as the under-developed law of non-international armed conflict and the lack of regulation of certain weapons.

Chapter 3 explains the types of armed conflict currently regulated under IHL, and the tests that have developed to determine whether an armed conflict exists. It explains that in the absence of a treaty definition of armed conflict, there are different views on what constitutes an armed conflict and when, therefore, the rules of IHL will apply. The application of IHL to other situations such as occupation and wars of national liberation is also covered. The chapter then turns to non-international armed conflicts; it describes the historical background from no regulation at all to their current regulation in Additional Protocol II, Common Article 3 to the Geneva Conventions and customary law. The tests for determining whether a non-international armed conflict exists are explained, and particular attention is given to the geographical scope of such conflicts. Finally, the chapter explains the various ways in which a non-international armed conflict can become internationalised, or transnationalised, and vice versa.

This is a general introduction to the book, explaining that the purpose of the book is to provide a concise but detailed explanation of the core rules of international humanitarian law. The contents of each chapter are summarised. It explains that the book looks at the major areas of IHL, putting them in historical context, so as to better understand how the law has evolved. This book also examines the current challenges for and pressures on the existing law, as IHL rules adopted in the time of cavalry and bayonets must adapt to deal with issues like drones, cyber warfare and autonomous weaponry. It notes that the third edition has been updated to reflect new developments in the law of armed conflict up to May 2023.

Chapter 4 looks at the concept of combatants and non-combatants, and its connected status, that of prisoner of war (POW). It examines who is entitled under IHL to combatant status, and examines those persons who have been denied combatant and POW status under IHL. Particular attention is paid to the status of resistance fighters, national liberation and guerrilla fighters, those participating in a levée en masse, and participants in non-international armed conflicts. The chapter outlines those categories of participant not entitled to combatant status such as spies, mercenaries, so-called unlawful combatants, and private military and security contractors. Chapter 4 also explores the current legal thinking regarding a contentious area of the law – that of civilians taking direct part in hostilities. The rules regarding POW status and the treatment of POWs are described. The chapter concludes by examining another developing area of the law: the power of detention in non-international armed conflicts.