In a security landscape characterised by the changing nature of armed conflicts and the proliferation of non-state actors, the problem of the applicability and enforcement of international humanitarian law poses a number of new controversial issues and fundamental challenges. Difficulties arise in clarifying the very notion of non-state actors; in defining whether and when they are parties to an armed conflict; in ensuring their adherence to relevant principles and rules of international humanitarian law; in preventing, prosecuting and sanctioning violations.