From a strict linguistic viewpoint, code-switching intertwines with a diverse range of language contact phenomena, from strict interference to several kinds of language mixture. Code-switching has also been addressed as an interactional phenomenon in everyday talk, an approach that implies a synchronic perspective. In this article, however, data are drawn from the records of communicative practices left behind by Catalan Jewish communities of the 14th and 15th centuries. These communities lived under well-defined cultural, political, and social conditions and displayed a rather complex linguistic repertoire of both linguistic resources and verbal genres. I analyze two of these verbal genres, which themselves must be viewed in the context of a broader Hispano-Arabic cultural tradition; they draw on a heteroglot background in which Semitic and Romance languages merged. In this analysis of the functions that code-switching played in these verbal practices, a contrast emerges between the use of code-switching and lexical borrowing (or alternation vs. insertional types of code-switching) in both verbal genres. This has implications for a much debated issue – the alleged existence of a medieval Catalan Jewish language – and challenges the idea that forms of linguistic practice must always be reduced to a bounded code.