The ELS aimed to study both continuity and change in the social and political life in Estonia between 1966 and 1991. Participants of the longitudinal cohort included over 1,700 Estonians born in 1948. Participants completed a baseline survey in 1966, when they were in their final year of high school. This cohort was interviewed several times until 1979. In 1991, a new phase of the ELS began, and the original cohort was reinterviewed. A cross-sectional cohort was added, including non-Estonians who were also in high school in 1965 to 1966 and the firstborn children of the original and non-Estonian cohorts.