The reformer Martin Luther repeatedly claimed that three educated Jews had visited him in Wittenberg and discussed certain passages of the Old Testament with him, particularly the semantics of עלמה in Isaiah 7:14. The authenticity of this claim is disputed, however, as there were hardly any Jews living in Saxony in Luther's time. This article will show that Luther's access to Jewish tradition was instead primarily due to written sources: the Latin excerpts from Jewish commentaries by Nicholas of Lyra and Paul of Burgos, early Christian Hebraistic literature, but above all the First Bomberg Rabbinical Bible printed in 1517. A case study of Isaiah 7:14 and 9:1-6 in Luther's lecture on Isaiah (1527) and his lecture on Isaiah 9 (1543/44) shall demonstrate that „the Jews" Luther argued against, were literary antagonists, constructed from these written sources. The paper will try to demonstrate that is it thus unlikely that Luther ever met any Jew in person and that his account of doing so is probably fictitious.