The Avon Longitudinal Study of Parents and Children (ALSPAC) is a transgenerational prospective observational study investigating influences on health and development across the life course. It has collected information on genetic, epigenetic, biological, psychological, social and other environmental exposures in relation to a diverse range of health, social and developmental outcomes. Recruitment sought to enrol pregnant women in the Bristol area of the UK during 1990–92. There were 13 761 women (contributing 13 867 pregnancies) recruited. This was extended to include additional children eligible using the original enrolment definition up to the age of 18 years. The children from 14 541 pregnancies were recruited in 1990–92, increasing to 15 247 pregnancies by the age of 18 years. The resource comprises a wide range of phenotypic and environmental measures in addition to biological samples, genetic and epigenetic information and linkage to health and administrative records. The study is celebrating its 21st Anniversary this year and over 700 peer-reviewed articles have been published using data from ALSPAC. The study has made contributions to understanding across a range of disciplines, exposures and outcomes. The presentation will present my view of the key contributions the study has made to date.