Criminal punishment for violations of the laws of war date to the earliest formal codifications. In particular, the Lieber Code of 1863 contained a large number of references to criminal punishment, which ultimately influenced a large number of the subsequent treaties. This said, initial codifications of the laws and customs of war after Lieber but before the Geneva Conventions of 1949 made only scant reference to individual criminal liability. Nonetheless, the grave breaches regime emerged in 1949 as an important response to the sufferings of Second World War. The idea behind the regime was that certain offences were sufficiently grave to warrant explicit codifications as war crimes. The development of grave breaches was then continued in 1977, first by the inclusion of further offences within Additional Protocol I, then by inclusion of the grave breaches regime within the Statute of the International Criminal Court. As a general rule, this development has nonetheless involved developing rules to deal with the horrors of the past. Potentially, history will serve as a helpful guide for countering the numerous challenges that face grave breaches in the future.