‘Due diligence’ or ‘vigilance’ is a substantial law obligation which requires that the state take all reasonable efforts within its power to prevent and repress the commission of internationally wrongful acts by others, ie non-state actors or other states. The duty of due diligence in general international law has its origin in the law of neutrality and the protection of foreigners from injuries occurring in civil wars. This general international law standard has been further interpreted and developed in the domain of armed conflict. The article argues that the due diligence concept, as it applies in the law of armed conflict (LOAC), developed certain specificities as to its content, particularly with regard to the importance of the interests to be protected and the extension of the concept to non-state actors. In the Corfu Channel and the Genocide (Bosnia and Herzegovina v Serbia and Montenegro) cases, the ICJ defined the due diligence standard as an obligation of conduct and specified certain factors influencing the required degree of diligence, without limiting it to specific branches of international law. Another remarkable impact of LOAC is the extension of the scope of subjects bound by due diligence duties to individual commanders, armed opposition groups, and international organisations. Both of these developments in LOAC, that is the specificities in the content and the addressees of the due diligence obligations, have contributed to the contemporary interpretation of the due diligence standard in general international law and to the subsequent re-interpretation of LOAC in the light of the latter.