In the last few decades, the role and status of armed non-state actors (ANSA) have become essential topics of analysis and discussion in order to better understand current international humanitarian law (IHL) and international human rights law (IHRL) dynamics. One issue is related to the reasons why ANSAs are bound by international law. A classical approach to the traditional theory of sources of international law relies on the consent given by States to be bound by an international rule. When dealing with ANSAs, however, the reasons why they are obligated by both IHL and IHRL lie beyond merely accepting the existence of their obligations. While some views take into account their consent, others are based on their relationship with territorial States and the rules previously accepted by States’ authorities. Implementing one or the other is not merely an intellectual exercise, and which alternative is taken will certainly have a direct impact on the effectiveness of international law as perceived by ANSAs.