War crimes are serious violations of international humanitarian law and the laws or customs of war committed in the context of an armed conflict, whether international or non-international. They include the murder of civilians, the indiscriminate killing of combatants or other persons not taking part in hostilities, the willful destruction of civilian buildings, the wilful causing of great suffering to body or health (including inflicting permanent disfigurement) of one or more persons not taking active part in hostilities, the deportation or forcible transfer of population, the extermination, enslavement or involuntary transfer of children and all acts of torture or cruel treatment.

The concept of war crimes has only relatively recently emerged as a central issue for governments and militaries around the world, following World War II. Before then, it was largely accepted that the horrors of war were just part of life and the behaviour of soldiers was determined by what they were ordered to do and by who eventually won the conflict. It was almost always possible for politicians and military leaders to escape punishment, although individual commanders and senior soldiers were often captured and prosecuted.

The definition of war crimes in international law, as formulated in the 1949 Geneva Conventions and their 1977 Protocol 1, differs depending on whether a conflict is international or non-international. The International Criminal Court prosecutes individuals for core international crimes under international law – war crimes, genocide and crimes against humanity – but these crimes may also be prosecuted in national courts that have made them a crime under their domestic criminal laws.