Starting with peaceful protests of people demanding democratic reforms and fundamental rights from the regime in Damascus, the Syria crisis developed into a full-fledged civil war causing largescale death, injury, and displacement. During the first year of the crisis, violence in Syria was marked by the brutal crackdown of regime forces on protesters. Confronted with a high degree of violence from state forces, opposition groups gradually organized politically and militarily. This article focuses on international legal obligations of armed opposition groups in the course of this crisis. Such obligations are clearly contained in international humanitarian law, and arguably also in international human rights law. In order to determine the applicable law, the classification of the situation as either an armed conflict or one of internal tensions and disturbances is fundamental but controversial. This article examines at what stage of the crisis international human rights obligations and international humanitarian law obligations of non-state armed groups became pertinent, and provides reasons why this is the case. It shall be argued that even before the Syria crisis turned into a non-international armed conflict, opposition groups were bound by fundamental rules of international human rights law. In addition to these rules, all parties to the armed conflict became bound by international humanitarian law once the situation reached a sufficient degree of violence, and the non-state groups a sufficient degree of organization. By examining the Syria crisis, this article shall show what these abstract criteria mean in practice.