A longitudinal study was conducted to determine factors predicting successful adoptions before placement and to identify differences and similarities between adoptive and biological families. Data collected on both adopted children and on their adoptive families before placement was related to data collected on the same children and families 6 months after placement and when the children were 2, 5, and from 8 to 12 years of age. Similar data to be collected on biological children and their families then provided the basis for an analysis of likenesses and differences displayed by biological and adopted children and their families, as well as for examination of developments over time in both groups as related to earlier factors. The original sample was composed of five groups: the first four groups consisted of adopted children and their adoptive families, while the fifth consisted of biological children and their families. The sampling period extended over nearly 6 years, from late 1962 to early 1968. The present report concerns the biological child/family group and only one of the adoptive groups (260 white families who adopted white children placed for adoption at 24 months of age or younger). The first phase of the study focused on the first 5 years of the child's life, while the second phase of the investigation involved a series of self-contained studies directed toward the functioning of the adoptive families and their comparison groups. Findings of both phases are reported. (RH)