In The City of God, XI, 10, St Augustine claims that the divine nature is simple because ‘it is what it has’ (quod habet hoc est). We may take this as a slogan for the Doctrine of Divine Simplicity (DDS), a doctrine which finds its way into orthodox medieval Christian theological speculation. Like the doctrine of God's timeless eternality, the DDS has seemed obvious and pious to many, and incoherent, misguided, and repugnant to others. Unlike the doctrine of God's timeless eternality, the DDS has received very little critical attention. The DDS did not originate with Augustine, but I am not primarily concerned with its pedigree. Nor am I concerned to ask how the doctrine interacts with trinitarian speculation. I will have my hands full as it is. In Section I of this paper I shall provide a rough characterization of the DDS, indicate its complexity, and focus on a particular aspect of the doctrine which will exercise us in the remainder of the paper, namely, the thesis that the divine attributes are all identical with each other and with God. In section n I shall discuss Alvin Plantinga's recent objections to Aquinas' version of the DDS. I shall then offer a more detailed presentation of what I take to be Aquinas' version (section III), and recast it in terms of a theory of attributes which is significantly different from Plantinga's (section IV). Although the recasting of the doctrine will enable me to rebut Plantinga's objections (section v), it by no means solves all the problems of the DDS. In section vi I shall discuss the chief lingering problem facing a defender of the DDS.