Explainer
International Humanitarian Law: The Basic Ideas
A practical introduction to the laws of war: who is protected, what may be targeted, and why distinction, proportionality and precautions matter.
Reviewed 18 September 2026. This is an evergreen explainer; case-specific legal findings should be checked against the newest authoritative source.
In short: A practical introduction to the laws of war: who is protected, what may be targeted, and why distinction, proportionality and precautions matter.
International humanitarian law, or IHL, is the body of law that regulates armed conflict. It does not decide whether going to war was lawful. Instead, once an armed conflict exists, IHL limits how force may be used and protects people who are not, or are no longer, taking part in hostilities.
IHL applies because of facts, not labels
A government does not have to formally “declare war” for IHL to apply. Legal classification depends on the facts: for example, armed conflict between States, or sufficiently intense fighting involving organised armed groups. The rules that apply can differ between international and non-international armed conflicts, but core humanitarian protections exist in both.
Distinction
Parties must distinguish between civilians and combatants, and between civilian objects and military objectives. Civilians are protected against direct attack unless and for such time as they directly participate in hostilities. Civilian objects are protected unless they become military objectives under the applicable legal test.
Proportionality
Even when attacking a lawful military objective, a party must not launch an attack expected to cause incidental civilian death, injury or damage that would be excessive in relation to the concrete and direct military advantage anticipated. Proportionality is not a simple comparison of body counts, nor does it mean civilian harm must be zero.
Precautions
Parties must take feasible precautions in attack to avoid or at least minimise incidental civilian harm. This can include verifying targets, choosing means and methods that reduce risk, giving effective advance warnings when circumstances permit, and cancelling or suspending an attack if the legal conditions are no longer satisfied.
People hors de combat and persons in custody
Wounded fighters, shipwrecked personnel, detainees and people who surrender are protected. They must be treated humanely. Prisoners of war have a detailed protection regime in international armed conflicts, while detainees in other conflicts remain protected by common Article 3, customary IHL and other applicable law.
IHL is not a verdict on a particular incident
Applying a rule to a real strike can require information that is unavailable publicly: the target, intelligence available to the attacker, weapon characteristics, expected civilian presence and anticipated military advantage. CAWT can explain the rules and report authoritative findings, but should not convert an allegation into a legal conclusion without sufficient evidence.
Frequently asked questions
Is international humanitarian law the same as human rights law?
No. They overlap, but IHL is specifically designed for armed conflict while international human rights law applies more broadly.
Does IHL make war legal?
No. The rules governing whether force may lawfully be used between States are distinct from the rules governing conduct during an armed conflict.
Do armed groups have to follow IHL?
Yes. Non-State armed groups that are parties to an armed conflict are bound by applicable IHL even though they cannot become parties to the Geneva Conventions in the same way States can.