This book identifies the degree of organization required from non-state armed groups (i) to become party to an armed conflict and thereby bound by applicable international humanitarian law; (ii) to have possible human rights obligations; and (iii) to create a context in which international crimes can be committed. Part I identifies three principal criteria that any party to a non-international armed conflict—including decentrally organized armed groups, transnational groups, or cyber groups—must meet: it must be a collective entity with sufficient capabilities to engage in hostilities and the ability to ensure respect for basic humanitarian norms. Part II conceptualizes contemporary debate and international practice on the question of whether armed groups have human rights obligations. It suggests that the sources and scope of potential human rights obligations of armed groups are understood best on a spectrum, with consideration given to three categories: groups exercising quasi-governmental authority; groups exercising de facto control over territory and population; and groups exercising no territorial control. Part III 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 instigates or actually commits the crimes. In sum, this book shows that the requisite degree of organization of armed groups to have obligations under different fields of international law cannot be determined in the abstract. It depends on the specificities of each field of law and the circumstances of each case.