No single-sentence definition universally adopted in everyday language exists. There is, however, a widely accepted legal definition grounded in international law. A war criminal is a person who commits a serious violation of the laws and customs of war (international humanitarian law) that incurs individual criminal responsibility.

The authoritative legal framework comes primarily from:

• The Geneva Conventions of 1949 and their Additional Protocols
• The Charter of the International Military Tribunal (Nuremberg Charter, 1945)
• The Rome Statute of the International Criminal Court (1998)
• Customary international law

Definition under the Rome Statute (ICC)

Article 8 of the Rome Statute defines war crimes as serious violations committed during armed conflict, including:

Against civilians

• Intentionally targeting civilians
• Intentionally targeting civilian infrastructure (homes, hospitals, schools)
• Killing, torture, or inhumane treatment of civilians
• Taking hostages

Against prisoners of war or detainees

• Torture or cruel treatment
• Execution without trial
• Denial of fair trial rights

Prohibited weapons or tactics

• Using prohibited weapons (chemical weapons, certain explosives, etc.)
• Perfidy (e.g., feigning surrender to attack)
• Using human shields

Other grave breaches

• Deportation or unlawful confinement
• Extensive destruction not justified by military necessity
• Sexual violence (rape, sexual slavery, forced pregnancy)

Key legal elements

To qualify as a war criminal, generally:

1. An armed conflict must exist (international or internal).
2. The act must violate international humanitarian law.
3. The individual must bear personal responsibility, either by:
   • Direct commission
   • Ordering the act
   • Assisting
   • Command responsibility (failure to prevent or punish subordinates)

Important distinction

Not every unlawful killing in wartime is a war crime. Lawful combat between military targets is permitted. War crimes involve violations of rules designed to limit suffering and protect noncombatants.

Historical origin of the modern concept

The modern legal framework emerged after World War II, when the Nuremberg Tribunal declared:

Individuals have international duties which transcend the national obligations of obedience imposed by the individual state.

Plain-language summary

A commonly accepted plain-language definition is a person who commits serious violations of the laws governing armed conflict, such as intentionally harming civilians, prisoners, or other protected persons.