The Cognitive Function and Ageing Studies (CFAS) are population based studies of individuals aged 65 years and over living in the community, including institutions, which is the only large multi-centred population-based study in the UK that has reached sufficient maturity. There are three main studies within the CFAS group. MRC CFAS, the original study began in 1989, with three of its sites providing a parent subset for the comparison two decades later with CFAS II (2008 onwards). Subsequently another CFAS study, CFAS Wales began in 2011.