Private military and security companies (PMSCs) have been used in every peace operation since 1990, and reliance on them is increasing at a time when peace operations themselves are becoming ever more complex. This book provides an essential foundation for the emerging debate on the use of PMSCs in this context. It clarifies key issues such as whether their use complies with the principles of peacekeeping, outlines the implications of the status of private contractors as non-combatants under international humanitarian law, and identifies potential problems in holding states and international...