This dissertation shows how Carolingian writers, as they reflected on the sacraments, and particularly on baptism, were led to distinctive understandings of politics, government, society, and culture. It helps to recenter scholarly understanding of a key development in the course of Western Civilization: the establishment of Christendom, or as they termed it, the Imperium christianum. Carolingian leaders conceived of their world and the people in it through a conceptual framework derived from the sacrament of baptism. Whatever Christendom has come to mean in popular understanding, it was for the Carolingians the society of the baptized. I study the religious metaphors and theological concepts which underlie the political and social ideas common to a variety of early medieval texts including law codes, theological treatises, land charters, ethical instruction, ritual commentaries, chronicles and other narrative sources. Careful study of early medieval books, especially how early medieval writers juxtaposed different genres of literature structured to privilege the implications of baptism, strengthen my argument and ground my study in the material culture of the early Middle Ages. Scholars have long described the Carolingians as militant Christians and religious reformers. My study will be the first to identify the aims of the Carolingian reform program by unlocking the religious discourse common to a wide array of sources produced in diverse centers over more than a century.