Last checked: 16 October 2026. Part of our Explainers series.
In brief: International humanitarian law (IHL) sets the rules of war. International human rights law (IHRL) limits what states may do to people at all times. International criminal law (ICL) makes the worst violations crimes for which individuals can be tried. “War crime”, “crime against humanity” and “genocide” are legal categories with specific elements, and each claim should be read with the standard of proof behind it.
Words like “war crime” and “genocide” carry great moral weight, and they are often used loosely. This guide explains the three bodies of law behind them, the legal definition of each crime, and the steps between an allegation and a conviction. We use the same distinctions in our own reporting; see our Methodology.
Three bodies of law
International humanitarian law: the rules of war
The International Committee of the Red Cross (ICRC) defines IHL as “a set of rules that seeks, for humanitarian reasons, to limit the effects of armed conflict” (ICRC, What is international humanitarian law?). It protects people who are not, or are no longer, taking part in hostilities, and limits the means and methods of warfare. It is also called the law of war or the law of armed conflict.
IHL governs how a war is fought (jus in bello). Whether a state was entitled to use force in the first place (jus ad bellum) is a separate question, governed by the UN Charter. As the ICRC puts it, IHL does not decide whether starting a conflict was legitimate; it regulates behaviour once the conflict has begun. Its core treaties are the four Geneva Conventions of 1949 and their Additional Protocols, alongside the Hague Conventions and customary rules that bind all parties.
International human rights law: limits on the state, at all times
IHRL sets out the rights that states must respect, protect and fulfil for everyone in their jurisdiction. Its main treaties include the International Covenant on Civil and Political Rights (ICCPR) and the International Covenant on Economic, Social and Cultural Rights, which build on the Universal Declaration of Human Rights.
The ICRC explains that human rights law “applies at all times, in peace and in war”, while IHL applies only in armed conflict (ICRC, IHL and human rights law). In an emergency, a state may suspend some human rights obligations, but not certain fundamental ones. The ICRC lists these as including the right to life, the prohibition of torture, the ban on slavery, the principle of legality, and freedom of thought, conscience and religion.
How the two fit together
In wartime both bodies of law apply. The International Court of Justice addressed this in its 1996 advisory opinion on nuclear weapons, saying the protection of the ICCPR does not cease in wartime, except where a state lawfully derogates. It returned to the point in its 2004 advisory opinion on the wall in the Occupied Palestinian Territory. In the 1996 opinion the Court also said that whether a killing in hostilities is an “arbitrary” deprivation of life is judged by the law that applies in armed conflict, meaning IHL.
International criminal law: individual guilt
IHL and IHRL mainly impose duties on states and parties to a conflict. International criminal law adds personal liability: it allows individuals, including commanders and heads of state, to be prosecuted for the gravest violations. The main code today is the Rome Statute of the International Criminal Court. National courts can also try these crimes. Our guide ICC vs ICJ explains which court handles which kind of case.
The three atrocity crimes
| Crime | Core element | Must there be a war? | Main definition |
|---|---|---|---|
| War crime | A serious violation of IHL | Yes, linked to an armed conflict | Rome Statute Art. 8; Geneva Conventions |
| Crime against humanity | Acts committed as part of a widespread or systematic attack on civilians | No | Rome Statute Art. 7 |
| Genocide | Acts committed with intent to destroy a protected group, in whole or in part | No | Genocide Convention Art. II; Rome Statute Art. 6 |
War crimes
War crimes are serious violations of the laws of war. Article 8 of the Rome Statute lists them, including grave breaches of the Geneva Conventions such as wilful killing, torture and hostage-taking, as well as intentionally attacking civilians, attacking hospitals or using starvation as a method of warfare. The act must be connected to an armed conflict, international or internal. A single act can be a war crime; no pattern is required.
Crimes against humanity
Under Article 7 of the Rome Statute, acts such as murder, extermination, deportation, torture, rape, persecution and enforced disappearance become crimes against humanity when committed “as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack”. No war is needed, so this category is often central in reporting on peacetime repression.
Unlike genocide, crimes against humanity have no dedicated global treaty. In 2019 the UN International Law Commission adopted draft articles on their prevention and punishment. The UN Office of Legal Affairs records that, by resolution 79/122 of 4 December 2024, the General Assembly decided to convene a conference to negotiate a convention, with sessions planned for 2028 and 2029.
Genocide
The 1948 Genocide Convention defines genocide as specific acts “committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such”. The acts are killing members of the group, causing serious bodily or mental harm, inflicting conditions of life calculated to bring about its physical destruction, imposing measures to prevent births, and forcibly transferring children (UN Office on Genocide Prevention, definitions). The UN Treaty Collection lists 154 parties as of our check.
What sets genocide apart is the special intent to destroy the group itself. Mass killing alone does not meet the definition, and intent is usually the hardest element to prove. Political and social groups are not covered by the Convention’s list.
From allegation to conviction: the standards of proof
The same event can be described as a crime at several stages, each with a different meaning. Under the Rome Statute:
- Allegation. A victim, witness, journalist, rights group or government says a crime occurred. Report it as a claim, attributed to whoever made it.
- Investigative finding. UN commissions and fact-finding missions usually report “reasonable grounds to believe” that violations or crimes occurred. This is a serious, evidence-based conclusion, but it is not a court verdict.
- Arrest warrant. ICC judges issue a warrant if there are “reasonable grounds to believe” that a person committed a crime (Article 58).
- Confirmation of charges. Before trial, judges must find “substantial grounds to believe” the person committed each crime charged (Article 61).
- Conviction. Guilt must be proved “beyond reasonable doubt” (Article 66). A conviction can still be overturned on appeal.
The phrase used tells you which stage has been reached. “Amounts to crimes against humanity”, from a rights group or a UN commission, is a legal assessment by that body. “Convicted of crimes against humanity” is a final or appealable court judgment.
Quick guide: which word should a reporter use?
- Use “human rights violation” for conduct by a state or its agents that breaches a human rights obligation, in peace or war.
- Use “IHL violation” or “alleged war crime” for conduct in an armed conflict that breaches the rules of war, and say who makes the allegation.
- Use “crime against humanity” only when the source says the acts were part of a widespread or systematic attack on civilians.
- Use “genocide” only for claims about intent to destroy a protected group, and name who is making the determination: a court, a government, a UN body or a rights group.
How we apply this
Our reports on Iran, the United States, Africa and Russia’s war in Ukraine name the source of every legal characterisation and the stage it represents. If you think we have used a term wrongly, tell us through our Contact page.
Additional sources
- ICRC, Fourth Geneva Convention (1949), text and commentary, on the protection of civilians.
- UN Office of Legal Affairs, Audiovisual Library: Genocide Convention, with an introductory note on its history.
- Legal Information Institute, Cornell Law School, international humanitarian law, a short reference definition.
- International Court of Justice, Bosnia and Herzegovina v. Serbia and Montenegro, the leading case on state responsibility under the Genocide Convention.