The Harmonised Cognitive Assessment Protocol (HCAP) is part of the Healthy Cognitive Aging Project, a study examining how people's memory and thinking change as they get older. In England, HCAP is a sub-study of ELSA, the English Longitudinal Study of Ageing (ELSA), a longitudinal survey of ageing and quality of life among older people that explores the dynamic relationships between health and functioning, social networks and participation, and economic position as people plan for, move into and progress beyond retirement. (The main ELSA study is held under SN 5050.) ELSA-HCAP1 took place in 2018 and interviewed ELSA core members aged 65 and over. It included a second, shorter interview with an informant, a family member or friend nominated by the ELSA core member to complete an interview on their behalf. ELSA-HCAP2 took place in 2023 and interviewed ELSA-HCAP1 sample members and additional ELSA core members aged 65 and over, and also included an informant interview. The HCAP study originated with the Health and Retirement Study (HRS) in the United States, which is a sister study to ELSA, a longitudinal study of people aged 50 and over in the United States. Researchers on HRS developed the protocols for HCAP, in discussion with researchers from ELSA and other international studies, and fieldwork in the United States began while ELSA-HCAP in England was still in the planning stages. The aim of ELSA-HCAP is to measure the prevalence of dementia and cognitive impairment among older people in the ELSA panel, in order to: Understand more about how widespread these conditions are in England and increase our understanding of dementia;Test how well the cognitive assessments used in this study can identify these conditions.Examine the 5-year change in cognitive function in the subset of respondents who take part across multiple waves of ELSA-HCAP.  HCAP scores developed by Alden Gross and colleagues - February 2024 For the third edition (February 2024), harmonised general and domain-specific cognitive scores were added from HCAP studies across six countries: China, England, India, Mexico, South Africa and the USA. The harmonised cognitive function scores have been developed by Alden Gross and colleagues. These scores empirically reflect comparable domains of cognitive function among older adults across the six countries, have high reliability and are useful for population-based research. The accompanying documentation includes a guidance file and the publication by Gross et al. (with supplement) that explains the scores and how they were derived. Each of the 1,273 participants in HCAP1 has a score on general cognitive function, executive function, language, orientation, and memory. ELSA-HCAP2 and Family and Friends (Informant) data deposited - February 2025 For the fourth edition (February 2025), the ELSA-HCAP2 and Family and Friends (Informant) 2023 data and documentation were deposited. The ELSA-HCAP2 dataset contains 2,022 cases and the Family and Friends (Informant) dataset contains 1,807 cases. Data were collected between April to November 2023 for ELSA-HCAP2 and April to December 2023 for Family and Friends (Informants). ELSA-HCAP2 had an additional aim; to examine the 5-year change in cognitive function in the subset of respondents that took part in ELSA-HCAP1 in 2018. Users should note that the data submitted currently contains no survey weights, and the technical report is not yet available. Both elements will be added in due course. Attention/concentration; language; memory; orientation; recall; recognition.