The recruitment, enlistment and use of children younger than fifteen to participate actively in hostilities is prohibited in customary international law as well as in several international legal instruments. The use of child soldiers is, despite of the prohibition, a widespread phenomenon with 300 000 as the estimated number of child soldiers in national armies as well as in various rebel and insurgent groups in the world today. Although the problem is world-wide; most recent focus have been on Africa where children have served and still serve in ongoing conflicts in various functions including but not limited to front line soldiers, messengers, guards and sex-slaves. Many of the world‟s child soldiers are girls that are facing the risks of sexual abuse and discrimination. In this thesis the 1996-2002 civil war in Sierra Leone will serve as an example of a conflict were children were used as soldiers.Prohibition against the use of child soldiers can be found in international legal instruments in both human rights law and international humanitarian law. It can also be found in instruments in the fields of international labor law and prohibition against slavery. The provisions differ in their definition of a child soldier; concerning age limit as well as the child‟s function during the conflict. There are also differences in the responsibility of states to protect children against being used as soldiers. This particularly affects girl soldiers since they often have their primary tasks behind the front line and thus are not usually included in the more narrow definitions of child soldiers.Two courts; the International Criminal Court (ICC) and the Special Court for Sierra Leone (SCSL) are used as examples of enforcement mechanisms. The SCSL as being the first court to deliver convictions for the use of child soldiers as well as thoroughly discussing the illegality of the use of child soldiers has been of importance in the fight against the use of child soldiers. The ICC will be the enforcement mechanism of the future and it has already prosecuted for the use of child soldiers. The SCSL has raised the awareness and started the struggle against impunity for those responsible for using child soldiers but it is the ICC that will have to continue the fight, although with some obstacles to overcome.