In the popular imagination, heresy belongs to the Christian Middle Ages in much the way that the Crusades or courtly culture do. Non-specialists in the medieval field may assume that the problem of heresy always existed, uniformly, throughout the period. But as Matthew Gillis shows in Heresy & Dissent in the Carolingian Empire: The Case of Gottschalk of Orbais (Oxford University Press, 2017), in the age of Charlemagne and his descendants, heretics were largely “seen as either distant foreign dangers or the legendary villains of ancient church lore.” That is, until around 840 CE, when one Gottschalk of Orbais began preaching what he called twin predestination. Gottschalk was heavily influenced by Augustine, who had argued that long before time began, God already ordained who would be among the elect and who among the damned. Gottschalk’s twin predestination theology made him into a figure Professor Gillis refers to as a “religious outlaw,” a “heretic in the flesh,” the Carolingian Empire’s foremost religious dissenter. Heresy & Dissent in the Carolingian Empire is a fascinating study of a figure whose meaning has been debated for centuries, but whose own moment in the 840s reveals a world beset with fears of sin and pollution. Matthew Gillis is Assistant Professor of history at the University of Tennessee, Knoxville.