Personhood in dementia centres on recognising and treating the person with dementia as a person first and foremost. Supporting personhood is a key goal of person-centred care models and a key principle in Irish dementia policy and formal care regulation. However, there is ambiguity around the concept in policy and practice. In particular, there is difficulty in moving from conceptual understandings of personhood to practical manifestations of it. In Ireland, there is little evidence to show that personhood is being supported in practice. This thesis seeks to reduce the ambiguity around this concept by examining how personhood in dementia is conceptualised, expressed, facilitated and actualised in formal care in Ireland. It aims to explore the core elements of personhood and provide guidance to policy and practice in how it can structure formal care provision and formal care relationships around personhood. The thesis involves three studies. The first analyses personhood in Irish policy-making through a content analysis of the Irish National Dementia Strategy and public submissions made in its development. The second study examines personhood within dementia care settings through a systematic review and qualitative evidence synthesis on the perspectives of people with dementia. The third explores personhood within dementia care relationships, using a multiple perspective research design on the perspectives and experiences of personhood of, people with dementia, family carers and formal carers. There are five key findings: reducing ambiguity around personhood, supporting core elements of the self, nurturing important relationships, managing change and managing care arrangements. Policy and practice need to focus on reducing ambiguity around personhood in dementia through additional training and education for formal carers. It also must ensure that formal care provision supports the core elements of the self and empowers people with dementia to maintain important relationships. In practice, this means designing care around the person with dementia, their interests and preferences, relationships and the social self. Formal care should also serve to mitigate the impact of change on people with dementia, particularly the impact of care settings, by adhering to ageing in place where possible and practicable, as well as ensuring that care settings do not deny or undermine personhood. However, in Ireland, supporting personhood requires a paradigm shift, from a supplier led, system-centred model to a person-centred biopsychosocial model of care which focuses on the person with dementia. Ultimately, supporting personhood should not be a goal to aspire to, rather it should be the foundation on which formal care provision is built.