This paper briefly introduces the aims and results of the Dutch longitudinal TRAILS study, as well as other study characteristics such as the specific measures that are included in the study, the non-response and attrition and the make-up of the sample. It is stated that the overall objective of the study is to contribute to the understanding of the determinants of adolescents’ mental (ill-)health and social development during adolescence and young adulthood, as well as the mechanisms underlying the associations between determinants and these outcomes. Some major results of the TRAILS study are discussed. Several strands of studies are highlighted. Firstly, there have been psychometrically oriented studies using latent class analyses on several psychopathological outcomes for distinguishing different classes of psychopathological symptoms across several specific types of disorders. Secondly, there have been a number of studies assessing (candidate) endophenotypic profiles in the cohort. Thirdly, several studies assessed associations between temperament and mental health in the cohort. Finally, a group of studies concerned social relationships in and around the classrooms, expressed for instance in bullying versus victimization of bullying, antisocial versus prosocial behaviour and classroom social status. The purpose of the paper is to bring the TRAILS study under the attention of international researchers who might learn from our experiences gained throughout the process of conducting the TRAILS study, and/or who might want to collaborate in the future.