This book explores the determining factors of Celtic mercenarism through a multidimensional approach, going beyond traditional stereotypes. Through a rigorous analysis of ancient sources and an anthropological perspective, it sheds light on the warrior culture and patronage system of Celtic societies. Contrary to the idea of mercenarism linked to poverty, the engagement of warriors was often motivated by elitist aspirations and the quest for prestige. By also examining property structures, succession, the ver sacrum, migrations, and political crises, the book offers new perspectives on the social and economic dynamics influencing the development of mercenarism.