Can rebel courts be lawfully established under international humanitarian law? Should their decisions be recognized within the principle of ne bis in idem according to international criminal law? By assessing these questions, the thesis undertakes a shift in perspective: So far, non-state armed groups and their representatives have primarily been regarded as potential perpetrators of international crimes, often committed during armed conflict. However, this book assesses and demonstrates that they can also be considered as euqal players in the enforcement of international criminal law during armed conflict.