Abstract. This article traces the intellectual history of scientific studies of intercessory prayer published in English between 1965 and the present by focusing on the conflict and discussion they prompted in the medical literature. I analyze these debates with attention to how researchers articulate the possibilities and limits medical science has for studying intercessory prayer over time. I delineate three groups of researchers and commentators: those who think intercessory prayer can and should be studied scientifically, those who are more skeptical and articulate the limits of science around this topic, and those who focus primarily on the pragmatic applications of this knowledge. I analyze these contests as examples of what Thomas Gieryn calls “epistemic authority” as medical researchers engage in what he describes as “boundary-work” or “the discursive attribution of selected qualities to scientists, scientific methods, and scientific claims for the purposes of drawing a rhetorical boundary between science and some less authoritative residual non-science.” (Gieryn 1999, 4 (Gieryn 1999, 4)).