The twin study project at the University of Helsinki began in 1974 with the Older cohort in order to investigate genetic and environmental determinants of common, complex diseases and their behavioural risk factors in Finland. Later also Finntwin16 and Finntwin12 studies have been initiated. The follow-up study has been proceeded to this day. Several studies have also been completed to some smaller cohorts. Currently, the Twin Study project is lead by Professor Jaakko Kaprio, and the research group is cooperating with many Finnish and foreign researchers.