This thesis investigates aspects of Medieval settlement on the Coigach Peninsula, through the study of archaeological deposits exposed in a deflating sand dune system at Achnahaird Sands, near Achiltibuie, Ross and Cromarty, North West Scotland. These dunes contain extensive evidence of past human settlement and industrial activity spanning the 4th to 19th centuries, most of which dates to the transitional period between the Medieval and post-Medieval periods (16th -17th century). The preservation of significant occupation deposits spanning this time frame is unusual within the existing context of the West Highlands, and clearly has broader implications for understanding settlement patterns in Northern Scotland in general. The investigation has two principal aims: 1. The detailed study of existing sources of information on Achnahaird Sands. 2. The examination of the implications of this information for the identification and interpretation of Medieval settlement in the Western Highlands in general. The study assesses the existing research context of Medieval or Later Rural Settlement (MoLRS) studies, and compares information relating to the geomorphology, history and archaeology of the dune system. The core of the study consists of the analysis of artefacts collected fi'om within the dune system since its archaeological discovery in the 1960s. The evidence indicates that Achnahaird was a place of importance during the Medieval period, until the abandonment of occupation within the dune system in the 1680s. Historical sources document its pre-eminence within the region during the 16th century as the residence of the tacksman of the 'Davoch of Aird', an administrative district encompassing the entire Coigach Peninsula, and subsequent decline in the late 17th century due to climatic deterioration and absentee ownership by the MacKenzie clan. The archaeological remains in the dune system demonstrate the existence of a separate industrial and commercial zone on the coastal fiinges of the settlement of Achnahaird, which is as yet unprecedented in Highland archaeology. The study concludes that this type of settlement is unlikely to be unique, but the circumstances within which the settlement remains have been preserved and exposed are highly unusual in the current archaeological record. The recognition of these circumstances has important implications for the further study of Medieval archaeology in the Highlands, given the paucity of evidence for stratified or securely dated occupation deposits. To date the only Highland site that offers comparable information is the unpublished Medieval settlement remains at the Udal, North Uist, though parallels also lie with a 16th century baile at Finlaggan, Islay and in recent excavations at Portmahomack, Easter Ross. The study has questioned the applicability of accepted definitions of the 'Medieval' period to the north western Highlands, and argues that the tag 'post-Medieval' can only be used unreservedly in the aftermath of the 1745 rebellion. The study also postulates that over time, settlement at Achnahaird has been broadly confined to an 'occupation zone' defined primarily by landform and proximity to the coast, with two major breaks in the sequence resulting fi-om climatic deterioration at the end of the Bronze Age and the reorganisation of settlement following the Highland clearances. Although the main settlement node (or nodes) have not been identified within this zone, the historical and archaeological evidence from the peripheral dune system suggest some form of semi-continuous occupation of this zone between c.319 and 1820 AD. The thesis concludes with suggestions for future research, focusing on the continued investigation of the archaeology of Achnahaird Sands, and broader themes that should be explored on a regional basis, including the relationship between trade and industry in the Medieval Highlands.