This 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. [Hebrew character]Azariah, 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.