Tens of thousands of contractors work for private military and security companies (PMSCs) during armed conflict and occupation, often hired by states to perform activities that were once the exclusive domain of the armed forces. Many of the obligations and standards that guide states in regulating their armed forces are lacking in relation to PMSCs, raising concerns that states might simply outsource their military policy to PMSCs without taking adequate measures to promote compliance with international humanitarian law (IHL). This article argues that the universally applicable obligation 'to ensure respect' for IHL in Common Article 1 of the Geneva Conventions can provide a key mechanism for addressing these concerns. Adapted from the source document.