How and why do non-state actors, in particular rebel groups, use international norms in their discourse? What are the patterns of that usage? Are they echoing or contesting these norms? These are the main questions under examination in this study, which lies at the nexus of several fields of research, drawing its concepts and theories from each of these. This chapter provides the interdisciplinary theoretical underpinnings of this research, using literature from four different areas: international norms, legitimacy, social movements, and rebel groups and civil wars. The literature provides a guide for how the norms may come to affect the actions and discourse of rebel groups, offers insight into the potentially strategic thinking and cost-benefit analysis behind the adoption of certain norms in the discourse, and suggests why rebel groups may adopt the language of international norms to frame their struggle or contest the norms either directly or through omission. Before examining the literature, the following section reviews definitions used throughout this book.