Does international law make individuals responsible for perpetrating war crimes during internal armed conflicts? Eve La Haye explores the content of international criminal law applicable in such conflicts and questions the 1995 finding of the Appeals Chamber of the International Criminal Tribunal for the Former Yugoslavia that responsibility could be enforced on the basis of customary international law. This finding is evaluated with regard to state practice and the practice of international organisations. The means to enforce individual criminal responsibility for such crimes are also investigated. The states on whose territory the crimes took place have sometimes tried such perpetrators, but can other states prosecute perpetrators of war crimes under the principle of universal jurisdiction? The applicability of universal jurisdiction to war crimes committed in civil wars and the practice of domestic courts are examined, alongside the role and achievements of prosecutions carried out by international courts and tribunals.