The Northern Ireland Longitudinal Study (NILS) is an important element in the ESRC data infrastructure for population and public health research in Northern Ireland and across the constituent countries of the UK. It has strategic relationships with the other UKCenLSs and, within Northern Ireland, with the Northern Ireland Statistics and Research Agency (NISRA), the Public Health Agency (PHA), and the Honest Broker Service (HBS). Its 28% sample, which combines census data with administrative data from the healthcard register, social care, and housing, will span the period 1981-2021 when the link to the 2021 Census is completed. This enables the description and analysis of changing populations in changing places, individual fortunes over the life course, household contexts, as well as progress between successive generations. The grant will fund, until 2025, the NILS Research Support Unit (NILS-RSU) which has the functions of maintaining a secure data laboratory for users to work on these data safely, of supporting users from project application to publication, of promoting NILS-based research to policymakers and the public, of seeking new users through the promotion of the NILS, and of encouraging research for the public benefit. A major highlight of our work programme will be testing, using and developing research around the 2021 Census link. The NILS-RSU will also seek to widen the social and educational base of the NILS in Northern Ireland through engaging with new stakeholders and growing its contribution to education. It will also encourage research using the NILS and the other UK longitudinal studies to contribute to national and international research agendas whilst developing new research partnerships in Northern Ireland.