The growth in scope and importance of the private military and security industry in the past decade has challenged the role of the state as the main provider of defence and security functions. At the same time it has put under stress the state's authority to properly oversee the conduct of private contractors and has raised the question of whether existing rules of domestic law and international law are adequate to ensure their accountability in the event of abuse. This book addresses this question through the lens of international human rights law and international humanitarian law. It presents a systematic analysis of the way in which these two bodies of international law, applicable in times of peace and in the event of armed conflict, may be interpreted and implemented in a way so as to fill possible accountability gaps. Human rights and humanitarian law obligations are analysed from the point of view of their applicability to the states involved, to international organisations, and to the companies and their individual employees. Victims' access to civil remedies and the criminal prosecution of private contractors, as well as new policy issues, such as the use of private contractors in the fight against piracy, are also covered in the book.