The manuscript sources for the Petrucci motet anthologies will likely remain a mystery. Although a few northern Italian manuscripts show varying levels of relationship to the first printed books of motets, readings of the concordant works from sources originating outside northern Italy are often highly diverse, most often suggesting an absence of familial relationship. On the other hand, several later manuscripts and printed sources document a strong connection with Petrucci’s anthologies, some of which most likely served as exemplars for these sources. Some extant Italian manuscripts that predate or are contemporaneous with the Venetian anthologies contain readings that are related to Petrucci’s, placing the motet books strongly within the sphere of northern Italian transmission. The author also delineates the impact Petrucci’s books had on the transmission of the early-sixteenth century motet.