John Behr probes the teaching of Irenaeus on divine simplicity. Behr cautions against viewing divine simplicity as a philosophical or theological element that Irenaeus settles prior to his engagement with the scriptural economy of salvation. He warns that to understand Irenaeus’ approach in this way would separate “theology” and “economy” in a manner that supposes that the former does not arise fundamentally from the latter. Behr sets forth briefly the metaphysical principles upheld by the doctrine of divine simplicity. The question that Behr raises, in light of Irenaeus’ approach, is whether divine simplicity merely comes from human speculation, absent the need for biblical revelation; or whether the doctrine is a grammatical rule; or (his Irenaean solution) whether in fact divine simplicity is inseparable from the way that God has revealed himself. Behr argues that the last‐named answer is the only one that could befit Irenaeus. In this light, Behr sets forth the careful exposition of Irenaeus’ doctrine of divine simplicity that has been provided by the patristics scholar Eric Osborn. While Behr is not oblivious to the erudition of Osborn’s account, Behr points out that unlike Osborn, Irenaeus never offers a distinct “refined theism” before proceeding to scriptural revelation. Thus, Behr argues that to understand Irenaeus on divine simplicity will require refusing to impose our categories of thought upon him, and instead carefully tracing the way in which Irenaeus reads Scripture.