What are war crimes?
War crimes include serious violations of the 1949 Geneva Conventions and other serious violations of the laws or customs of war defined in Article 8 of the Rome Statute. They are one of the international crimes (crimes under general international law), which also include the crime of genocide, crimes against humanity and the crime of aggression.
War crimes can be divided into two types:
a) grave breaches of the Geneva Conventions of 1949, namely wilful killing, torture, causing suffering, deportation of the population, taking hostages, etc.;
b) other serious violations of the laws and customs of war (deliberate attacks on the civilian population and objects, personnel and transport of humanitarian aid, killing and wounding belligerents who laid down their weapons, improper use of the enemy's flag, deliberate attacks on religious, cultural, historical sites, hospitals, a statement that there will be no mercy, looting cities, etc.) (Article 8 of the Statute of the International Criminal Court).
More information in the section "Questions and Answers" of the site and in the section "Sources of International Humanitarian Law".