In this lecture, we confront some basic conceptual and philosophical issues in the science-religion question: What are the legitimate means of acquiring sure knowledge, and what are sources from which we can obtain such knowledge? The answers invoke faith and reason as the means and “God’s Two Books” (the Bible and the created world) as the sources. Here, we examine approaches to these means and sources in the Christian tradition, foundationally in St. Augustine’s 5th-century writings and more recently in the important 1998 encyclical Fides et ratio.