The paper will firstly examine the relationship between private companies, armed conflicts and IHL. The second and third sections will in turn analyse the content and the extent of the obligation of corporate due diligence in armed conflicts and post-conflict settings, as well as the legal liability of both the personnel of private companies and private companies as such. The Draft Treaty and the ILC Draft Principles represent important contributions in addressing the corporate liability and fill a gap under IHL: while pursuant to the latter, the responsibility of individuals who commit war crimes is well established, corporate liability is indeed still in an infancy stage in international law.