The SIBS is a study of adoptive and biological siblings and their parents, aiming to understand how siblings interact and influence each other and how the family environment impacts psychological health. The sample consists of adoptive and non-adoptive families with adolescent siblings. All families lived within driving distance of the University of Minnesota in the United States, and had adolescent siblings with no more than a 5-year age gap and no physical or mental handicaps. All adoptive families in the study have both an adoptive adolescent aged between 11 and 21 who had been placed in the home before the age of 2, as well as a second adolescent biologically unrelated to the adopted adolescent. The sample contains over 1,200 adolescents and 1,100 parents from 617 families (409 adoptive and 208 non-adoptive) within Minnesota's Twin Cities greater metropolitan area.