How does U.S. law treat citizenship for children born abroad to one U.S. citizen parent?

1. The statutory framework: Congress, INA sections, and the principle of descent

Congress has created a statutory regime, rooted in the INA and shaped by the Child Citizenship Act and subsequent amendments, that governs when a foreign-born child of a U.S. citizen acquires citizenship through a parent rather than by birth on U.S. soil; courts have long held that citizenship by descent is a matter of statute, not common law ^{[1] [2] [5]}.

2. Acquisition of citizenship at birth: married parents and physical‑presence tests

When a child is born abroad in wedlock and at least one parent is a U.S. citizen, the child generally acquires citizenship at birth if the U.S. citizen parent met statutory physical‑presence or residence requirements before the child’s birth — current rules for children born on or after November 14, 1986, typically require the U.S. citizen parent to have been physically present in the United States for five years, two of which were after the parent’s 14th birthday ^{[3] [4] [6]}.

3. Out‑of‑wedlock births and special paternal requirements

For children born out of wedlock the law treats mothers and fathers differently in practice: a U.S. citizen mother can often transmit citizenship under the usual physical‑presence rules, while a U.S. citizen father must meet additional paternity, legitimation, and support‑obligation steps — for example, evidence of blood relationship, an agreement to provide financial support, or court legitimation and forms such as DS‑5507 where paternity must be established ^{[3] [7] [4] [8]}.

4. Citizenship after birth: INA sections 320/322 and automatic acquisition on lawful admission

Children who do not acquire citizenship at birth may still become citizens before age 18 under INA provisions: a foreign‑born child admitted to the United States as a lawful permanent resident and residing in the legal and physical custody of a U.S. citizen parent can automatically acquire citizenship under 8 U.S.C. 1431 (INA 320) once statutory conditions are met, and INA 322 and the Child Citizenship Act of 2000 provide routes for children living abroad to naturalize or obtain certificates when a citizen parent and presence requirements are satisfied ^{[9] [1] [5]}.

5. Proof, process, and routine bureaucratic steps

Parents use diplomatic and administrative tools to document a child’s claim: a Consular Report of Birth Abroad (CRBA) from a U.S. embassy or consulate establishes that a child was a U.S. citizen at birth when qualifying conditions are met, and USCIS Form N‑600 (Certificate of Citizenship) or a U.S. passport serves as primary proof; agencies routinely request evidence of the parent’s U.S. citizenship and of physical‑presence timelines when deciding claims ^{[8] [10] [4] [7]}.

6. Edge cases, military presence, and limits of the law

The law contains nuanced exceptions and evolving guidance: time served abroad as a member of the U.S. armed forces or certain government service may count toward physical‑presence requirements in some instances, U.S. soil concepts exclude embassies and many bases for birthright purposes so acquisition depends on the parent’s status rather than the location of the hospital, and policy changes and judicial challenges have periodically reshaped interpretations — reporting and agency policy manuals reflect both settled rules and recent administrative clarifications ^{[6] [2] [11] [5]}.