Few in antiquity or Byzantium would have questioned that angels have power. Portraying that power, however, posed a special challenge for Byzantines. In a world where both language and image were bound up in materiality, angels captured all that could and could not be said of God. If Christ was understood to be the Word of God made flesh, then there might be license for making pictures of Christ, at least in his earthly guise. But what exactly were angels? More than human, yet known for fleeting visitations in human form; like God, but created by God. Both “subtle” in body and slippery in categorization, angels perplexed Byzantine artists and writers. Glenn Peers calls our attention to this tension between the materiality that representation demands and the incorporeality that defines angels in this nuanced monograph on attitudes toward angels in Byzantine devotion, art, and theology. Like the angels, Peers is a category-crosser himself: an art historian by training, he combines subtle understandings of Byzantine theology and polemics with judicious use of critical theory to illumine the problem of angels as a crisis of illusion and representation. Central to Peers’s study is the iconoclastic controversy, marked by intense polemic between those...