This article explores the interface of state responsibility, non-state actors, and the due diligence principle. It begins by examining the various principles of responsibility under international law. After doing so, it closely considers the deliberations of the International Law Commission on the topic of state responsibility. In light of these developments, attention is then paid to exactly what has been expected of states with regard to the activities of non-state actors during the last century. This overview focuses on the due diligence principle, a principle which, it is argued, can be restrictively or expansively interpreted, as the particular facts and circumstances require, to hold states responsible for their actions or omissions related to non-state actors.