The Immigration and Nationality Act (INA), put into force in 1952, is the law governing the modes of acquiring citizenship in the US. The American law applies both the ius soli and the ius sanguinis pursuant with the principles dictated in the Fourteenth Amendment of the US Constitution.
The US citizenship can be acquired either at birth or after birth. One may acquire citizenship at birth if he/she has been born in the United States or within certain territories or outlying possessions of the United States; or if he/she had a parent or parents who were citizens at the time of birth.
Citizenship after birth can also be attained by derivation or acquisition through parents, provided that the child is under 18 years of age and has at least one parent, including an adoptive parent, who is a US citizen by birth or naturalisation.
The Immigration and Nationality Act also defines the process of acquisition of US citizenship by naturalisation. To be eligible, the applicant must fulfil the requirements stated by law and must have resided in the US for at least five years prior to filing the application. The residential requirement is reduced to three years in case of naturalisation by marriage.
Most naturalisation applicants are required to take a test on English language and Civics (US history and government). Upon completion of the naturalisation process, new citizens are required to swear an Oath of Allegiance to the US.
The United States Supreme Court struck down most laws forbidding dual citizenship. Nowhere in US law is it now mentioned that a person of dual nationality has to choose between one citizenship and the other, meaning that although it does not formally recognize dual citizenship, the United States poses no restrictions on dual citizenship. US dual citizenship is therefore permitted. US dual citizens enjoy full benefits of US citizenship and citizenship of the foreign country. US dual citizens are fully entitled to the rights granted by their foreign citizenship, including the right to vote in the foreign country’s national election and running for public office in the foreign country. US dual citizens also owe allegiance to the US, as well as to the foreign country, and therefore they are bound and subject to the laws in both countries.