This chapter examines the centrality of early modern ecclesiastical history, written by Catholics as well as Protestants, in the refinement of research techniques and practices anticipatory of modern scholarship. To Christians of all varieties, getting the Church's early history right mattered. Eusebius's fourth-century history of the Church opened a royal road into the subject, but he made mistakes, and it was important to be able to ferret them out. Saint Augustine was recognized as a sure-footed guide to the truth about the Church's original and bedrock beliefs, but some of the Saint's writings were spurious, and it was important to be able to separate the wheat from the chaff. To distinguish true belief from false, teams of religious scholars gathered documents; the documents in turn were subjected to skeptical scrutiny and philological critique; and sources were compared and cited. The practices of humanistic scholarship, it turns out, came from within the Catholic Church itself as it examined its own past.