This is the introduction to the thematic issue Faithful to the Cross in a Moving World: Late Medieval Carthusians as Devotional Reformers. The editors discuss how the Carthusian order expanded in the Late Middle Ages and how, in contrast to the first Carthusians, new charterhouses were created in or close to the cities. The introduction studies how this change came about, connecting it to the order's origin in the monastic reform movement of the eleventh and twelfth centuries, the changing economy of piety in the Late Middle Ages, and developing ideas as to what was the best form of religious of religious life.