Iris Murdoch’s library included annotated volumes of or about medieval theology. She took medieval thought seriously, engaging actively with Anselm of Canterbury and Julian of Norwich, for example, and sharing both its metaphysical grandeur and its appreciation for the complexity of the moral life. This chapter explores resonances between Murdoch’s philosophical vision of the good, her sovereign concept, and the good life, and understandings of the same in medieval theology. It is divided into two parts. Part 1, on the idea of the ultimate good, examines connections with Anselm and another twelfth-century thinker, Peter Abelard. Murdoch’s concept of the good was similar to Anselm’s idea of a perfect being (namely, God), and both believed that moral growth meant participation in the standard of perfection. In turn, at a personal level, Murdoch shared with Abelard a quality of intellectual courage, as well as, philosophically, an appreciation of the mysteriousness of ultimate goodness. Part 2, on the moral life, draws upon additional insights from Augustine of Hippo and the wider field of medieval spirituality. Murdoch’s idea of the ‘fat relentless ego’ as the enemy of moral growth reflected the medieval concept of original sin, which was received from Augustine and carefully nuanced by Anselm. In turn, her call to supplant the ego by a process of unselfing, or redirected attention, with the assistance of a special energy, drew upon ideas of prayer and grace embedded in medieval religious practice. The chapter ends by asking what, if any, may be equivalent in Murdochian thought to the medieval attachment to eschatological hope.