The number of non-state actors, in the past not accountable for committing international crimes or violating human rights, is proliferating rapidly. Their ways of operating evolve, with some groups being increasingly fragmented and others organizing transnationally or in cyber space. As non-state armed groups are involved in the vast majority of todays armed conflicts and crisis situations, a new and increasingly important question has to be raised as to whether, and at what point, these groups are bound by international law and thereby accountable for their acts. Breaking new ground in addressing international human rights law, international criminal law, and international humanitarian law in one swoop, Rodenhäusers text will be essential to academics and practitioners alike.