He is the author of Medieval Philosophy: An Historical and Philosophical Introduction (2007), Le temps, l’éternité et la prescience de Boèce à Thomas d’Aquin (2005), Boethius (2003), and Early Medieval Philosophy, 480–1150 (2nd rev. ed. 2002). He has edited Abelard’s Collationes for Oxford Medieval Texts (2001) and is the general editor of The Cambridge Companion to Boethius (2009). His influential essays on the medieval reception of Aristotle and Plato were collected in Aristotelian Logic, Platonism, and the Context of Early Medieval Philosophy in the West (2000).