Justice requires that public policy improve the lives of disadvantaged members of society. Dementia is a source of disadvantage, and a growing global public health challenge. This article examines the theoretical and ethical connections between theories of justice and public dementia policy. Disability in general, and dementia in particular, poses important challenges for theories of justice, especially social contract theories. First, the article argues that non-contractarian accounts of justice such as the Capabilities and Disadvantage approaches are better equipped than their contractarian counterparts to analyse issues of justice and dementia. Secondly, using a capabilities framework, I analyse original empirical data from qualitative interviews and discussion groups with health and social care professionals. The article concludes that social connection is a ‘fertile functioning’—a multiplier of advantage that enables people to live well with dementia together—and should therefore be a priority for public dementia policy.