Centuries of contact between Older Scots and the Scandinavian language of Norn, coupled with geographic isolation, has resulted in the highly distinctive dialects spoken in the Orkney and Shetland Isles today. In this chapter, we document the socio-historical context which led to the formation of these dialects, and look to a range of studies which describe these dialects’ lexical, phonological and morphosyntactic forms. We note forms shared with other varieties of Scots but concentrate mostly on the highly localised features not found in mainland Scotland. In addition to broad comparisons between Orkney and Shetland, we also document the dialect diversity within each location. Finally, we turn to bidialectalism, and specifically how speakers may have access to two ‘codes’ in their linguistic repertoire, where Standard Scottish English is used alongside localised vernaculars, and how this might impact on dialect attrition in the coming years.