Working from a monastic cell in Paris, French polymath and savant Marin Mersenne became a key facilitator of the early scientific revolution. An interdisciplinary music theorist, Mersenne drew from the burgeoning field of rhetoric to describe, analyze, and teach musical structures. At a time when the heart of seventeenth-century rhetoric seemed to be firmly in Germany, Marsenne's writings demonstrate that these phenomena extended far beyond those borders. Universal Harmony in the Age of Eloquence uses Mersenne's work as a case study to examine the exchange between music and rhetoric in early modern music theory. Author Andre de Oliveira Redwood argues that, although features of Mersenne's writings have often been dismissed as stylistic defects or signs of muddled thinking, they reflect a deliberate rhetorical approach and an epistemological posture consistent with principles of sacred invention. Mersenne's Harmonie universelle serves as a prime example, demonstrating that the affinities between musical and rhetorical thought exist precisely because they are grounded in mathematics and the physical properties of sound. An important contribution to our understanding of seventeenth-century French music and culture, Universal Harmony in the Age of Eloquence offers a new vision of scientific and musical inquiry undertaken in the service of theological reflection.