https://www.childwelfare.gov/
National Survey of Adoptive Parents:
http://aspe.hhs.gov/hsp/09/nsap/index.shtml
Chapin Hall Center for Children: a research center at the University of Chicago that produces policy-related research on child welfare and foster care.
http://www.chapinhall.org/
Donaldson Adoption Institute: an independent and objective adoption research and policy organization whose website contains research reports on a range of adoption topics.
http://adoptioninstitute.org/
Primary longitudinal studies related to adoption:
National Survey of Child & Adolescent Well-being
http://www.acf.hhs.gov/programs/opre/research/project/national-survey-of-child-and-adolescent-well-being-nscaw
Minnesota-Texas Adoption Research Project
http://www.psych.umass.edu/adoption/
Early Growth and Development Study
https://www.egdstudy.org/
National Survey of Family Growth
http://www.cdc.gov/nchs/fastats/adoption.htm
Leiden Longitudinal Adoption Study
https://openaccess.leidenuniv.nl/handle/1887/25253