Written broadly within a Lexical Functional Grammar Framework, this thesis provides a descriptive and theoretical account of definiteness in Insular Scandinavian from a synchronic and diachronic perspective. Providing evidence from Ancient Germanic to Old Norse to Modern Faroese, it is argued that the weak feature on the adjective has an important part to play in the historical narrative of definiteness marking in Faroese, alongside more traditional elements like the bound and free definite articles and demonstratives. Each of the features is read within the context of its nominal syntax and it is observed that there are recurrent pathways of change which each time result in the growth of syntactic structure and the redistribution of features. One of my principal findings for the Old Norse period was that the noun phrase had developed a FOC slot to the left edge of phrase. It is this focus domain which helps to explain the distribution of definiteness markers and which provides an account for the grammaticalization of the free and bound marker hinn. It is also this focus domain which eventually leads to the development of dedicated definite slots in the prenominal space and eventually to functional DP projection in Modern Faroese. This thesis provides new and detailed descriptive data on the definite noun phrase in Modern Faroese, a lesser studied Insular Scandinavian language. Since Faroese is widely reported to have 'lost' the genitive case in recent times, the above changes are read against a background of morphosyntactic change. A key finding of the thesis for the Modern language is that Faroese is becoming increasingly reliant on analytic marking, despite the fact that is is still a highly inflected language. It is this reliance on syntax which has rendered the genitive redundant, not, as has been suggested, the 'loss' of case which has led to the development of periphrastic alternatives.