This paper aims to describe the use of the definite article in Medieval Sardinian in order to outline the typology of this feature and to determine its stage of grammaticalization. In particular, I analysed the Ancient Logudorese scripta. To reach this aim, I took into account both the functional and formal dimension of analysis. The data, obtained by quantifying all the occurrences of the definite article in a certain class of texts, show a clear, progressive increase of the definite article through the different registers of the language and in different pragmatic, semantic, syntactic, and textual domains during the whole period of time taken into account.