Despite the early recognition by Eusebius that Irenaeus quoted Hebrews in works which are now lost, scholars have been less willing to see the Letter making its mark in Adversus haereses. Although there are exceptions, some, for example, acknowledge the presence of Hebrews 1:3 in book 2, views to the contrary are stated plainly. It is difficult to find contemporary confidence in Irenaeus’s use of Hebrews in his extant writings and most deny it a place in his “canon.” Even if recognized, the place of the Epistle in Irenaeus’s constructive theology is minimized. In this paper, an analysis of Irenaeus’s knowledge and use of Hebrews, I hope to begin a challenge to such opinions. I don’t intend here to insist that Irenaeus revered Hebrews as a sacred text, the same way in which he sees the Spirit speaking through the prophets, the evangelists, and Paul. But I do wish to demonstrate that his thought is dependent in important degrees upon its language and teaching. Hebrews 1:3, 8, 9, 2:10, 3:4, 5, 5:9, 14, and 8:5 contribute in important ways to his view of creation as the act of the Father with his Son and Spirit; the uniqueness of the Father and Son; his notion of martyrdom; the contrast between the true God and the idols; Mary’s recapitulation of Eve; anthropological immaturity and need for progressive growth to maturity; and a hermeneutical framework for his understanding of the relationship between the two economies, between prophecy and fulfillment, between the Law and grace, the earthly and the heavenly. I will conclude, that although perhaps in a different manner than Eusebius knew it, Adversus haereses also provides evidence of the important place of Hebrews in the work and possibly the canon of the bishop of Lyons.