This article traces how early Christian thinkers (including Irenaeus, Eusebius, Epiphanius and Jerome) conceptualised ‘Jewishness’ in bibliographic terms. The material that early Christian sources associate with the Gospel according to the Hebrews exhibits a substantial textual relationship with the Gospel according to Matthew. The distinction emerges within a fourth- and fifth-century heresiological project of bibliographic categorisation that seeks to differentiate Jewish and Christian books and readers. Bibliography is a way of distinguishing reading communities and thereby advances the late ancient rhetorical project often known as the parting of the ways between Judaism and Christianity.