The thesis offers a synthetic overview of the hymns of Ambrose of Milan in the context of fourth-century doctrinal song and Ambrose's own mystagogical preaching. Both settings, I argue, are integral to the interpretation of Ambrose's hymnodic project. The hymns, I maintain, employ sophisticated poetic techniques to foster a pro-Nicene sensitivity in the bishop's embattled congregation. After a summary presentation of early Christian hymnody, with special attention to Ambrose's Latin predecessors, I argue for the mystagogical function of fourth-century songs. I then examine Ambrose's sermons, especially his catechetical and mystagogical works, for preached parallels to this hymnodic effort. Close reading of Ambrose's hymnodic corpus (fourteen hymns, of which thirteen, I maintain, are authentic) constitutes the bulk of the study. I corroborate my findings through a treatment of early Ambrosian imitations, especially the poetry of Prudentius. These early readers, I maintain, amplify the hymnodic features that I identify as mystagogical. Engaging the mass of literature on Ambrose, early Christian hymns and poetry, and doctrinal dispute in the fourth century, I make several contributions to the scholarship in the course of my dissertation. First, particular and original readings of words, phrases, and hymns contribute to the ongoing project of deciphering Ambrose's meaning. Second, I contribute to the emerging consensus on the authenticity of thirteen hymns as genuinely Ambrosian. Third, close attention to the early reception of Ambrose's hymns illuminates both Ambrose's methods and the influences shaping the expansion of popular hymns and learned Christian poetry in the early Latin church. Fourth, drawing on these findings I can offer a theological reading of the corpus of Ambrose's hymns, a project often ignored in scholars' attention to specific features and hymn-texts. Last, I locate that theology in the context of Ambrose's wider thought, contributing in some part to our appreciation of Ambrose the creative thinker and innovative pastor. Although hardly exhaustive, my dissertation thus represents a rare attempt to read Ambrose's hymns as a body of literature transmitting his distinctive, pro-Nicene theology.