Legitimacy is generally a term that is associated with the state. The term surfaces when there are problems with state legitimacy, when it is lacking or absent. This present volume attempts to think through the relevance of the concept of legitimacy for other political actors than the state. Rebel groups, in the shape of insurgents, terrorists, warlords and guerrillas, are all engaged in a process of claim making as legitimate actors representing certain political agendas and constituencies. We are interested in dissecting the processes of the emergence of legitimacy in contexts of disorder and conflict. Legitimacy is not only a belief or belief system that informs social action, it is also a practice with a repertoire of legitimacy claiming, reinforcing, copying and emulating elements. Governance provision is an important legitimacy generating activity, just as it has been in the formation of states. The volume, however, points out that there are many more aspects to legitimacy that deserve attention. The contributors draw on a wide variety of cases and in-depth investigation, to bring forward individual and micro-level dynamics related to legitimacy claims, as well as bringing forward the often-times problematic role of external actors when it comes to legitimacy and illegitimacy dynamics. The chapters in this book were originally published in a special issue in Small Wars & Insurgencies.