CFAS Wales is a longitudinal study looking at health and cognitive function in older people living in Wales. The study builds on the design and infrastructure of the Cognitive Function and Ageing Study collaboration (CFAS) exploring biomarkers and other early indications of risk of cognitive decline, such as imaging. It also investigates factors that may delay the onset of dementia, specifically focussing on the role of bilingualism and social networks and allow a more in-depth examination of rural-urban variations, which have been markedly unexplained in previous studies.