This paper analyzes the linguistic repertoires of Jews in the Low German-speaking areas in the first decades of the 20th century, as a contribution to historical sociolinguistics. Based on fieldwork questionnaires held in the archives of the Language and Culture Atlas of Ashkenazic Jewry (LCAAJ), it addresses the question of whether the Jewish minorities spoke a supralectal form of standard German or Koiné forms of dialects, relating this to issues of language shift from Western Yiddish. The study shows that many Jews living in northern Germany during the 1920s and 1930s still had access to a multilingual repertoire containing remnants of Western Yiddish; that a majority of the LCAAJ interviewees from this area emphasized their excellent command of standard German; and that their competence in Low German varied widely, from first language to no competence at all, depending on the region where they lived.*