In the course of two and a half centuries, the city-state of Rome rose from central Italian dominance to Mediterranean hegemony. Together with this transformation in the scale and extent of Roman power came a revolution in social, economic and cultural practices. My dissertation argues that the success of this imperial project and the nature of the social revolution it triggered must be understood by reference to Roman religious practices throughout this period. I set out the case for why and how religion in mid-Republican Rome and Roman Italy drove meaningful and highly consequential institutional change over time. A primary mover in this institutional change is trust: religious behaviors, observances, and rituals shaped the creation and perpetuation of the forms of trust that anchored the "quasi-voluntary compliance" regime binding together the citizen body of the expanding Republic and its constellation of allies. With the help of insights gleaned from sociology and political science, I isolate several specific areas through which this dialogue of religiously-mediated trust was promoted and enacted: temples and monumental construction; festivals and festival culture; numismatic iconography; and the announcement and expiation of prodigies. I show how these four domains of cultural practice--shaped and orchestrated according to religious considerations--became sites of institutional innovation, with implications for Rome's imperializing project. This characterization of the middle Roman Republic as a distinctive example of how religion interfaces with community-building, economic development, state formation, and imperial expansion aims to be of interest not only to Romanists and ancient historians but to political theorists, comparative historians, economic historians, and sociologists.