As several scholars have noted (in particular J. Geiselmann and J. McCue), the 11th Century debates about the presence of Christ in the Eucharist can be seen as a distinction between a more Ambrosian, and thus realist, approach, and a more Augustinian, and thus symbolic, approach. It was the burden of Berengar of Tours to justify his teaching in the light of the apparent opposition of Ambrose and thus to rely on the support of Augustine, whose De Doctrina Christiana, particularly Book III, seemed to support his own position. Lanfranc of Canterbury and Guitmund of Aversa, in their respective responses to Berengar, defended Augustine and attempted to interpret the controversial passage in De Doctrina III as harmonious with their realist understandings of the Eucharist. The essay analyzes the various ways that Berengar, Lanfranc and Guitmond used De Doctrina to support their positions, and argues that the crux of the debate turned on which side could buttress sufficient support from Augustine. This defense of De Doctrina III led, particularly in the thought of Guitmond, to the development of the possibility of holding that the Eucharist is both a sign and a reality, and that these two are not in opposition to one another. Although De Doctrina Christiana provided much of the vocabulary and conceptual distinctions used in later sacramental theology, it itself only explicitly discusses the sacraments on a few occasions. The Berengarian controversy, however, turned Augustine’s text on biblical interpretation into a sacramental text.