The Breakthrough Generations Study is a large-scale, long-term cohort investigation aiming to identify genetic, environmental, behavioural, and hormonal determinants of breast cancer and other women’s health outcomes. It began recruiting in 2004 and continued through 2011, enrolling over 110,000 UK women (aged 16–102) from across England, Scotland, Wales, and Northern Ireland. Participants were recruited primarily via invitation letters sent to women living in Britain, supported by publicity campaigns and celebrity endorsements. Participants completed detailed baseline questionnaires and provided blood and urine samples, with linkages to NHS records. Follow-up is conducted via self-completed questionnaires every 3–4 years, with plans to continue follow-up for at least the next 40 years and beyond.