The recent boom in private security raises the concern that states may simply outsource military and security activities to PMSCs without taking adequate measures to promote company compliance with international norms. In relation to their national military forces, states have clear obligations to take positive steps to ensure that soldiers respect international law and to investigate, punish and redress any violations that soldiers commit in the field. But what international standards exist to guide states’ actions in relation to PMSCs that they hire in armed conflict?