Defending persons accused of international crimes is not an easy task. Before the International Criminal Tribunal for Rwanda created for the purpose of prosecuting persons responsible of genocide and other serious crimes committed in Rwanda, defence lawyers face constraints of various kinds that have sometimes plagued their mission. This is particularly due to the institutional imbalance between the prosecution office and the defence, the inaccessibility to the scene of the crimes, the unavailability of defence witnesses, the almost exclusion of lawyers of Rwandan origin, and so on. The author argues that in the context of criminal prosecutions before international courts, defence should be recognized as an institution essential to the legitimacy of international criminal justice. To do this, he suggests some areas of improvements including, inter alia, the institutionalization of defence, an increased involvement of local lawyers as well as a budgetary autonomy which allows an effective organization of defence. In this way, the accused can effectively exercise their right to just and fair trials.