His work focusses on northwestern Europe, particulary France, England, and the Low Countries in the period from ca. 900 to 1250. He is the author of Day of Reckoning: Power and Accountability in Medieval France (University of Pennsylvania Press, 2004) and the co-editor of The Experience of Power in Medieval Europe, 950-1350 (Ashgate Publishing, 2005). From 2001 to 2006 he was co-editor of the The Medieval Review, an electronic book review journal for all fields of Medieval Studies with more than 2500 subscribers. Berkhofer, who earned his Ph.D at Harvard University, has received support for his current project from the American Philosophical Society and the Institute of Historical Research in London.