Music is central to the processional pilgrimage of El Rocío, which attracts hundreds of thousands of pilgrims to Andalusia, Spain, late each spring. The pilgrimage affords a unique view, in microcosm, of the relationships between music and ritual from both ritual-studies and ethnomusicological perspectives. Based on extensive fieldwork and other research, this dissertation explores the nexus of the Catholic ritual system in Andalusia, flamenco, and the specific music of El Rocío: the Sevillanas Rocieras. That nexus becomes clear through exploration of three particular features of the pilgrimage: (1) the devotional processions that generate a single, focused, collective emotion; (2) the Andalusian musical form called the palo; and (3) the informal musical gatherings called juergas, which take place nightly along the route. Analysis of structural and morphological relationships between ritual, music, and emotion yields surprising realizations about how these three elements come together as embodied aesthetics within a communitas to generate popular culture. Another important finding of this work is the necessity of placing, at the center of the inquiry, the religious experience—including the curious Andalusian phenomenon of the “chaotic” emotional procession and its role within the overall pilgrimage and ritual system. The dissertation concludes with two theoretical positions. The first addresses the process of “emotional structuring” and its role within the musical rituals of El Rocío and, by extension, Andalusia. The second advances a theory of ritual relations with potential application to ritual systems beyond Andalusia. The author presents both positions within an evolutionary framework based on the tenets of biomusicology, neurophenomenology, and Peircean semiotics.