This study complements and enriches scholarship on the role of mercenary soldiers in Byzantium and treats mercenary service as a social phenomenon. It investigates Byzantine concepts of mercenary service and compares them to the Western European ones. It analyses the economic, military and political factors that led to the increasing recruitment of mercenary soldiers in Byzantium and assesses the impact of the increasing professionalization of warfare in Western Europe on Byzantium. It discusses the organization and remuneration of groups of mercenaries and the effects grants of land, offices and titles had on the identity and motivation of mercenaries. It also examines the self-images constructed by mercenary warriors and the code of conduct that they observed and according to which they circumscribed their actions. In addition, the ideals and values promoted by mercenary soldiers are compared to those of the Byzantine aristocracy.