The Lothian Birth Cohort studies comprise three cohort studies, combining research in psychology, epidemiology, and gerontology. The Lothian Birth Cohort of 1921 investigated childhood intelligence, at age 11, and health outcomes in old age. The study included a group of 551 adults born in the Lothian area of Scotland in 1921. The publications that resulted from this study contributed to the emerging field of cognitive epidemiology. One of the most important findings of this study was that children with higher IQs at age 11 were not better protected against cognitive decline in later life. Instead, they had better cognitive ability in old age, attributable to greater stability in intelligence across their lives. The 1936 Lothian Birth Cohort Study is a similar cohort to the 1921 study, but includes 1091 participants born in 1936. The sample size was larger than the 1921 cohort, and more detailed information was collected on those born in 1936. Additional intelligence tests were administered to 1208 people born on the first day of the intercalary months of 1936, and detailed information on the home environment was provided. These additional data were collected annually for the following 16 years, and included home visits by the researcher. The Lothian Birth Cohort studies can provide information on the determinants of cognitive decline, because they have a measure of premorbid intelligence measured at age 11. They can also be used to provide information on health differences in old age, taking childhood factors into account. The 1921 Lothian Birth Cohort Study was funded by several UK research funding councils and other agencies. The 1936 Lothian Birth Cohort Study was funded by the charity Older People UK and the charity Help Older People, which has recently become part of the Unplugged Mind Project. The Lothian Birth Cohort Study is supervised by Professor Ian Derry in the Department of Psychology at the University of Edinburgh.