In the modern globalized world, so-called private military and security companies (PMSCs) are employed by a variety of actors in times of both war and peace. They perform a plethora of services for not only international organizations, NGOs, and multinationals, but also various States. It goes without saying that, especially in areas torn apart by armed conflicts, these corporations and their personnel can and sometimes do engage in different types of misconduct that may constitute violations of international law. There are still regulatory gaps in the national and international legal frameworks applicable to PMSCs, and the lines of responsibility often remain unclear. In light of this, State responsibility becomes an important instrument for attaining justice and ensuring respect for international law by private contractors. This book investigates the possibility of applying the doctrine of State responsibility to the employment of PMSCs in areas affected by conflicts and to breaches of international law committed by these companies and their personnel. It examines an array of circumstances in which the unlawful conduct of PMSCs and their staff may be attributed to States under international law and the extent of such attribution. The study further analyzes the application of positive obligations imposed on States and the scope of this application. (Series: School of Human Rights Research - Vol. 67) Subject: International Law, Humanitarian Law, Human Rights Law, Security Studies, Military Studies]