The medieval cartulary is well known as a major source for documents. This article takes Scotland as a case study for examining how the understanding of medieval cartularies has been shaped by those works extensively used by researchers to access cartularies and their texts – in a Scottish context this is principally the antiquarian publications and modern catalogues. Both pose their own problems for scholars seeking to understand the medieval cartulary. After an in-depth examination of these issues, a radical solution is offered which shifts the attention onto the manuscripts themselves. Such an approach reveals those extant cartularies to be fundamentally varied, and not an exclusive ‘category’ as such. This in turn allows historians to appreciate the dynamic nature of cartularies as sources for documents, and to eschew the deeply embedded tendency to see the cartulary simply as a copy of a medieval archive.