- Many foreign-born adopted children acquire U.S. citizenship as soon as they enter the United States. They do not need to formally apply (though they are entitled to a certificate of citizenship); they become citizens automatically.
- Other foreign-born adopted children may need to wait until they have satisfied certain criteria before they automatically acquire citizenship. Still others (those living abroad) may need to formally apply to "naturalize".
- Orphans adopted by a U.S. citizen parent are citizens once their adoption is final and they have lawfully entered the United States as permanent residents. Children who did not immigrate as orphans, but who were adopted by a U.S. citizen parent and obtained lawful permanent resident status also automatically acquire citizenship (so long as they meet all the criteria prior to their 18th birthday).
- Foreign children who are adopted by U.S. citizens who reside overseas are also entitled to citizenship, but under slightly different criteria. Such children may file for naturalization during a legal, temporary visit to the U.S. so long as they are under 18 and their parents or grandparents meet certain other eligibility criteria.
- Adopted children residing in the United States may file for a certificate of citizenship using U.S. Citizenship and Immigration Services (USCIS) Form N-600. Adopted children residing outside the United States may file for naturalization using USCIS Form N-600K.
Source: U.S. Citizenship and Immigration Services