Abstract: Many modern observers consider peer review an essential mechanism that protects the trustworthiness and quality of both scientific journals and scientific grantmaking. But how did the practice of refereeing originate, and how did it become tied to scientific legitimacy in the eyes of both scientists and laymen? Peer review is now so embedded in modern science that many observers have assumed external refereeing has been a consistent part of science since the Scientific Revolution. However, as this talk will show, the practice of refereeing did not truly develop until the 19th century, and for well over a hundred years refereeing was not seen as essential or even particularly important. It was not until the late 20th century that “peer review”—a term that first came into use in the 1960s and 1970s—became seen as a prerequisite for scientific legitimacy. The image of refereeing as an essential feature of science arose first in the Cold War United States in the wake of a series of political attacks on scientific funding. To head off attempts to require Congressional review for individual scientific grants, scientists and their supporters argued that peer review was a crucial process that ensured the credibility of science as a whole. This vision of peer review took hold with remarkable speed, and today, peer review is seen as a cornerstone of science.