jats:titleAbstract</jats:title>jats:pThis paper investigates code-switching and script-switching in medieval documents from the Cairo Geniza, written in Judaeo-Arabic (Arabic in Hebrew script), Hebrew, Arabic and Aramaic. Legal documents regularly show a macaronic style of Judaeo-Arabic, Aramaic and Hebrew, while in letters code-switching from Judaeo-Arabic to Hebrew is tied in with various socio-linguistic circumstances and indicates how markedly Jewish the sort of text is. Merchants in particular employed a style of writing devoid of Hebrew elements, whereas community dignitaries are much more prone to mixing of Hebrew and Judaeo-Arabic (and Arabic), although the degree of mixing also depends on a number of other factors, such as on the individual education. Analyses show great variation within the repertoire of single authors, as shown on the example of Daniel b. ʿAzariah, according to the purpose of the correspondence, with religious affairs attracting the highest Hebrew content, whereas letters pertaining to trade exhibit the lowest Hebrew content. Script-switching between Hebrew and Arabic may be prompted by convenience of individual writers, or occur as an idiosyncratic quirk, but reveal the close familiarity of the writer with both alphabets.</jats:p>