Although early Venetian operas by composers such as Claudio Monteverdi and Francesco Cavalli offer today's listeners profound moments of emotion, the complex codes of meaning connecting emotion (or affect) with music in this repertoire are different from those of later seventeenth-century operatic repertoire. The specific textual and musical markers that librettists and composers used to indicate individual emotions in these operas were historically and culturally contingent, and many scholars thus consider them to be inaccessible to listeners today. This dissertation demonstrates a new analytical framework that is designed to identify the specific combinations of elements that communicate each lifelike emotion in this repertoire. Re-establishing the codes that govern the relationship between text, musical sound, and affect in this repertoire illuminates the nuanced emotional language of operas by composers such as Claudio Monteverdi, Francesco Cavalli, Antonio Cesti, and Francesco Lucio. The new analytical framework that underlies this study derives from analysis of seventeenth-century Venetian explanations and depictions of emotional processes, which reveal a basis in their society's underlying Aristotelian philosophy. Chapters III and IV examine extant documents from opera librettists, composers, audience members, and their associates to reveal how they understood emotions to work in the mind and body. These authors, many of whom were educated by Aristotelian scholars at the nearby University of Padua, understood action and emotion to be bound together in a reciprocal, causal relationship, and this synthesis was reflected in the way that they depicted affect in opera. It also guided the ways that singer-actors performed and audiences interpreted this music. In contrast, post-1660 Baroque operas from France and Italy express affect according to the musical conventions of the Doctrine of Affections (based in the ideas of René Descartes) and aim to present a single, clear emotion for each large semantic unit (recitative or aria). This paradigm does not hold true for operas composed before 1660; thus, this vibrant repertoire requires a new analytical approach that respects its pre-Cartesian musical aesthetics. Early Venetian opera composers express not just one, but many affects in each semantic unit. In their operas, musical sound interacts directly with text and dramatic action on a line-by-line basis to produce an unprecedented fluidity of emotional meaning. Chapter II describes a new analytical framework based in this understanding to reveal the means that librettists, composers, and performers used to communicate emotion in this repertoire. Chapters V through X contain hermeneutic and musical analyses (according to the method described in Chapter II) of case studies drawn from Venetian operas performed between 1640 and 1658. These chapters illustrate how this repertoire uses a flexible but well-defined system of musical and textual markers to convey characters' emotions. This new approach unlocks an aesthetic system that privileges the fluid, real-time emotional reactions of the individual in accordance with Aristotelian emotional understanding. In Chapters XI and XII, supporting information gleaned from seventeenth-century acting treatises, reception documents, and conduct books enables an examination of the singer's role in depicting these textual and musical representations of affect in performance. These two chapters address seventeenth-century views on affective communication through voice acting and physical gesture, together with recommendations for today's singers who perform this repertoire. In taking a systematic approach to the identification of specific textual, musical, and gestural means for communicating affect in early Venetian opera, this dissertation offers a new approach to analyzing and performing its dynamic emotional content.