Guy Geltner is Professor of Medieval History at the University of Amsterdam and Director of The Center for Medieval Studies Amsterdam. His research focuses on the social, environmental, and religious history of the late Middle Ages, especially in an urban context. He has published The Medieval Prison: A Social History (2008); William of St. Amour's De periculis novissimorum temporum (2008), and Defenders and Critics of Franciscan Life (co-edited with Michael F. Cusato; 2009).