This thesis aims to identify the degree of organization required from non-state armed groups (1) to become party to an armed conflict and thereby bound by applicable international humanitarian law, (2) to have human rights obligations, and (3) to create a context in which international crimes can be committed. Accordingly, it is structured in three main parts. Part 1 identifies three principal criteria that any party to a non-international armed conflict needs to meet: it must be a collective entity with sufficient capacities to engage in hostilities and to ensure respect for basis humanitarian norms. Part 2 aims to conceptualize contemporary international practice regarding human rights obligations of non-state armed groups. It argues that the sources and scope of human rights obligations of armed groups are understood best if three categories of groups are considered: groups exercising quasi-governmental authority; groups exercising de facto territorial control; and groups exercising no territorial control. Part 3 examines the requisite degree of organization of armed groups to create contexts in which crimes against humanity or genocide can be committed. It argues that the degree of power and organization of groups behind these crimes depends on whether the group only instigates or also directs the crimes. This study concludes that the requisite degree of organization of armed groups to have obligations under different fields of international law or the ability to create contexts in which international crimes can be committed cannot be determined in the abstract. It depends on the specificities of each field of law and the circumstances of the case.