ALSPAC, also known as Children of the 90s, is a prospective, population-based birth cohort study. The study was designed to examine how genetic and environmental factors interact to influence health, behaviour, and development across the lifespan. Over 14,000 children born between April 1991 and December 1992 were initially included in the study from over 14,500 pregnant mothers recruited antenatally. ALSPAC participants were born to mothers residing in the Bristol & District Health Authority Area (Former Avon Health Authority Area) at the time of recruitment. Further recruitment occurred at age 7 years, with more than 450 additional children enrolled in the study. Similarly, between ages 8 and 18, more than 250 additional children were added to the cohort, and after turning 18, just under 200 additional children enrolled in the study. Data have primarily been collected from ALSPAC participants and mothers, but also from the mothers' partners and the children's fathers and grandparents.