The Latin source glosses in Cambridge, St. John's College MS L. i (J) and Cambridge, University Library MS Gg. 4. 27 (Gg)—two fifteenth-century manuscripts of Troilus and Criseyde—are, despite their probable Chaucerian origin, infrequently discussed by scholars of Chaucer's works, and still less frequently thought to hold interpretive significance. Yet, these glosses, like their counterparts in the Canterbury Tales, demonstrate a complex hermeneutic of ambiguity that promotes multiple, at times competing, interpretations of the English verse. This article traces the links between the Troilus and Canterbury Tales glosses, charting the evolution of this Chaucerian marginal hermeneutic. It reads the glosses in J and Gg as an experimental early step toward the more elaborate marginal apparatus in the Canterbury Tales, one that demonstrates the same potential for richly intertextual interpretive ambiguity.