In three distinct but related chapters, this dissertation explores the causes and consequences of an important trend in American religion -- the concentration of people into very large churches. I undertake a systematic examination of historical materials to excavate the origins of the modern Protestant megachurch and find its genesis lies in the beginnings of the Reformation, not in the late twentieth century as commonly argued. I then turn to study the consequences of this shift, using data from the combined National Congregations Study and U.S. General Social Survey. I uncover a significant negative relationship between congregation size and the probability of attendance. These results provide convincing evidence in support of the theory that social interaction and group cohesion lies at the heart of the size-participation relationship. Finally, I use zero-inflated regression models to examine the relationship between size and the socio-economic status composition of the church. My analyses reveal a negative relationship between size and low household income. Larger congregations contain a larger proportion of regular adult participants living in high income households and possessing college degrees, and a smaller proportion of people living in low income households. In congregations located in relatively poor census tracts, the relationship between high socio-economic status (SES) and congregation size remains significant. This research offers important correctives that help situate megachurches in the United States in their proper context. It provides important insights into how the shift of churchgoers into large congregations may concentrate power in these organizations and reduce overall rates of attendance.
