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Ireland has a fascinating history of ancient kingdoms and more modern migrations. Furthermore, Ireland’s island location at the north-western edge of Europe makes it conducive to genetic homogeneity and isolation. The impact of historical migrations on the island is largely unknown, as is the extent of genetic structure in Ireland, despite successful efforts to characterise such genetic ancestry and structure with uniparental data, and efforts within the neighbouring British Isles.The description of the impact of this history will aid both the understand of history within Ireland, but aid genetic disease research as understanding the genetic structure of the island will inform on the distribution of rare disease causing variants within Ireland. Additionally, a genetic isolate also exists within Ireland, the Irish Travellers. The genetic origins of this population are similarly unclear, with limited blood group loci suggesting a broad Irish origin. This population has an increased burden of recessive genetic diseases, diseases that are often present, but more infrequent, within the wider settled Irish population. Understanding the population genetics of this community will help elucidate their genetic origins as well as aid understanding of the genetic structure that these disease causing alleles are found on and thus aid medical research in the community. In in Thesis I describe the recruitment and analysis of two cohorts; one of regional extended settled Irish ancestry (the “Irish DNA Atlas”), and another of extended Irish Traveller ancestry. In conjunction with reference datasets I demonstrate; i) subtle but thorough structure across the island of Ireland, ii) the footprints of previous migrations in the north of Ireland and the north of Britain, iii) extensive structure within the Irish Traveller population and an estimated time since isolation from the rest of Ireland, and finally iv) a catalogue of rare genetic variation within 1,582 Irish individuals the use of this variation in exploring genetic structure and ancestry. These results describe the genetic landscape of Ireland and structure with the Irish Travellers for the first time. This structure will aid the research of genetic disease variants within Ireland and the Irish Travellers. It additionally helps elucidate the impact of Irish history on the genomic landscape of the island, which may be of interest to historians.