Murder, rape, slavery and torture have long been recognised as the worst crimes, and society has put tough measures in place to bring perpetrators to justice. But when such offences are committed on a massive scale by one group of people against another, courts have been less sure about what to do.
The series of international tribunals and special courts established over the past decade to deal with genocide and other crimes against humanity have achieved mixed results. Trials expected in coming months of Iraqi dictator Saddam Hussein and the leaders of Cambodia's Khmer Rouge are seen by some observers as being flawed.
Hopes are high for the Hague-based International Criminal Court, but there are even doubts about whether it can properly give justice to the people affected by conflicts.
Then there are situations like East Timor, where 1,500 civilians were killed, 250,000 displaced, and where rape and torture was widespread when Indonesian troops and proxy gangs and militias tried to prevent a move for independence in 1999. Tiny East Timor's government, not wanting to upset delicate economic and diplomatic relations with its giant neighbour, is resisting calls for an international tribunal.
Nonetheless, experts in international law believe that a system is evolving that will, over time, give justice to people who have suffered at the hands of their own governments or those from other countries. They warn, though, that finding the best approach is a matter of trial and error and could yet take decades.
Renowned lawyer and judge with the Special Court for Sierra Leone, Geoffrey Robertson, stressed last week that the world was at a 'very rudimentary stage in delivering on international criminal justice', having taken concerted steps only over the past 10 years.