Students of medieval Spanish literature can recognize oral tradition (= OT) as substrate, catalyst, reactant, and reagent in the verbal arts created in peninsular Romance vernaculars. Direct and indirect testimony confirm its decisive action on lyric and narrative tokens in those languages, as well as on paremiological forms such as refranes (“folk sayings”) and advinianzas (“riddles”). OT is a practical instrument, like the clay tablet, codex, or printed page, but exceptional among them: it warrants the singer to create variations within parameters of genre, performance, and audience. Field recordings made throughout the modern Hispanic-speaking world document reflexes of early romances, folktales, riddles, proverbs, villancicos, and folk remedies, as well as later corrido and decima forms. The multiple iterations, and the social networks that support them, reveal not immutable texts but bundles of narrative and poetic features diffused nonuniformly in space and time. In this sense the present can be used to explain the past. OT offers useful interpretive tools. Its anthropological, literary, and folkloristic dimensions account for artistic and cultural features—patterns of sound and rhythm, narrative self-dramatization, the performance arena enveloping performer and audience in which values of group identity are inculcated—unassayed by literalist methods. Medieval vernacular lyric, narrative, and prose share orality in their genesis, transmission, poetics, and aesthetics. To deny the role of OT in the continuum of epic and chronicle, in the corpus of romances, or in the tales common to enxempla, sermons, and clerical poetry is to obscure their primary verbal dimension and confound their cultural purpose. Adjacent literary traditions affirm the existence of OT in medieval Hispano-Romance before its emergence into vernacular