War crimes are serious violations of international criminal law. However, each new conflict, international or non-international, gives rise to the commission of war crimes. Why ? Does-it have factors that predispose to violent behaviours ? The 20th century is the century of international criminal law which is first characterized by the establishment of international military tribunals after the discovery of the atrocities of World War II, then international tribunals « ad hoc », eventually it ends by the introduction of an international criminal court. International Criminal Tribunals established for former Yugoslavia and Rwanda have permitted the application of International Conventions, defining armed conflict’s rules, to non-international armed conflicts. What was the impact of these tribunals’ case laws on war crime concept ? Eventually, even if the establishment of International Criminal Court gave hope to combat impunity, its status highlights the delicate balance between states’ sovereignty and the willingness of universal justice. Transitional justice was introduced to complete or to replace institutional justice in some cases. One of transitional justice’s objectives is to make a transition a transition between wartime and peacetime as smooth as possible even if many challenges remain. In fact, the fast restoration of lasting peace would it not be better ? The transitional justice leads us to wonder if we have to judge or forgive war crimes ?