HEAF is a cohort study investigating whether working to older ages is good or bad for health and how often health affects people’s ability to work in different types of job at older ages. Participants are patients registered with participating general practices, and general practitioners (GPs) reviewed the sampling lists before mailing and excluded patients whom they thought should not be approached (e.g. because of terminal illness or recent bereavement). Over 8,000 male and female participants aged 50-64 years were recruited from 24 general practices across England, and were followed annually for the first five years of the study, following initial data collection in 2013-14.