Regulating the conduct of businesses in armed conflicts: a due diligence perspective on private military and security companies in international humanitarian law

States’ employment of private military and security companies (PMSCs) in the context of armed conflicts for the provision of services and the consequent outsourcing of military and security activities raises multiple issues regarding the legal status of these businesses under international humanitarian law, as well as their eventual responsibility for international wrongdoing. For this reason, the present research investigates the current framework of international humanitarian law regulating PMSCs’ activities, with a focus on the characterisation of personnel as mercenaries, combatants or civilians. This article simultaneously explores international and national instruments aimed at providing a regulatory framework for PMSCs, as well as self-regulatory initiatives and codes of conduct developed in an extra-governmental context. Eventually, by adopting a due diligence perspective, this contribution evaluates the possibility to attribute the responsibility for PMSCs violations of international law to the state for omissions in undertaking due diligence obligations with respect to private actors’ conduct.