This article investigates a particular armed opposition groups’ behavior: detentions during hostilities. This is an important concern since these non-state actors repeatedly deprive persons of liberty during armed conflicts. Interestingly, international humanitarian law (IHL) does not explicitly address such actions, thus seemingly leaving them to be regulated by the domestic law of the State concerned which, in general, only authorizes its own agents to carry out such acts. Therefore, armed opposition groups could never detain individuals legally in a non-international armed conflict. Nonetheless, this can be inconsistent in the application of the principle of equality of belligerents, which affirms that all parties to an internal armed conflict have the same scope of rights regardless of their cause. In the following pages, a number of arguments focusing on real-life scenarios will be presented in order to show that, despite not being explicit, armed opposition groups are logically and implicitly authorized by IHL to detain individuals who are engaged in an armed conflict against them.