United States nationality law details the conditions in which a person holds United States nationality. In the United States, nationality is typically obtained through provisions in the U.S. Constitution, various laws, and international agreements. Citizenship is established as a right under the Constitution, not as a privilege, for those born in the United States under its jurisdiction and those who have been "naturalized". While the words citizen and national are sometimes used interchangeably, national is a broader legal term, such that a person can be a national but not a citizen, while citizen is reserved to nationals who have the status of citizenship.

Individuals born in any of the 50 U.S. states, the District of Columbia or almost any inhabited territory are United States citizens (and nationals) by birthright. The sole exception is American Samoa, where individuals are typically non-citizen U.S. nationals at birth. Additionally, individuals born from foreign diplomats working in the United States are neither citizens nor nationals. Foreign nationals living in any state or qualified territory may naturalize after going through the legal process of qualifying as permanent residents and meeting a residence requirement (normally five years).

Nationality defines the legal relationship between a person and a state or nation, specifying who is a member or subject of a particular nation. The rights and obligations of citizenship are defined by this relationship, as well as the protections to which nationals are entitled. Though nationality and citizenship are distinct and the United States recognizes the distinction between those who are entitled or not entitled to rights, its statutes typically use the words "citizen" and "citizenship" instead of "national" and "nationality". The Constitution of the United States did not define either nationality or citizenship, but in Article 1, section 8, clause 4 gave Congress the authority to establish a naturalization law. Before the American Civil War and adoption of the Fourteenth Amendment, there was no other language in the Constitution dealing with nationality.

The first statute to define nationality and naturalization in the United States was the Naturalization Act of 1790. It limited those who were eligible to be nationals as free, white persons. Following the practices of English common law, the legal system of the United States absorbed coverture, or the assumption that a woman's loyalty and obligations to her spouse were more important than her loyalty and obligation to the nation. While the Nationality Act did not forbid a woman to have her own nationality, judicial rulings and custom on domestic matters established that infants, slaves, and women were unable to participate in public life, as a result of the belief that they lacked critical judgment and had no right to exercise free will or control property. Native Americans were considered to be subjects of foreign governments and per decisions like Dred Scott v. Sandford (60 U.S. (19 How.) 393, 1857) were only eligible to become naturalized if they assimilated white culture. From 1802, only fathers were able to pass on their nationality to their children. The Naturalization Act of 1804 confirmed that a woman's nationality was dependent upon her marital status and the Naturalization Act of 1855 tied a wife's nationality, and that of her children, to her husband's. A wife who married a foreign husband in this period was assumed to have suspended her nationality in favor of his. She was able to repatriate upon termination of the marriage and resumption of residence in the United States. While the 1855 Act specified that foreign wives gained U.S. nationality, the law created confusion as to whether it required American women who married aliens to take the nationality of the spouse. For example, Nellie Grant, daughter of President Ulysses S. Grant, reacquired her U.S. nationality in 1898 by an Act of Congress, after a divorce from a British husband.

In the aftermath of the Civil War, Congress enacted the Civil Rights Act of 1866 and later that year passed the Fourteenth Amendment to the United States Constitution to grant citizenship status to former slaves. The language of the Amendment was race-neutral and granted nationality to anyone born in the United States and subject to their jurisdiction. It did not extend nationality to Native Americans. In Elk v. Wilkins (112 U.S. 94, 1884) the Supreme Court confirmed that those Native Americans who were born subject to tribal jurisdiction did not have birthright nationality in United States territory.

Under the Insular Cases of 1901, the Supreme Court ruled that unincorporated territories and insular possessions of the United States, which were not on a path toward statehood, had limited applicability of the U.S. Constitution. At the time, these included Guam, the Philippines, and Puerto Rico, acquired in 1898 at the end of the Spanish–American War. According to the decision, those born in insular possessions or unincorporated territories were not eligible for citizenship, though they were considered nationals and could hold a U.S. passport and gain diplomatic protection from the United States. Passage of the Expatriation Act of 1907 eliminated the uncertainty created in 1855, definitively stating that marriage solely determined all women's nationality. The law immediately revoked the nationality of married women, regardless of whether they were born in the United States or naturalized, if they were married to a non-citizen. It was retroactive and did not require a wife's consent, leaving many women unaware that they had lost their nationality.

The federal Immigration Acts of 1921 and 1924 were passed by Congress to address the concern that white authority was declining. The 1921 Act, known as the Emergency Quota Act, restricted immigration from various countries. The limits applied to foreign husbands and children of U.S.-born women, but provided an exemption for foreign wives and children of birthright male nationals. In 1922, the Cable Act was passed, declaring that an American woman could not be denied the right to naturalize because she was married. It established procedures for women, who had previously lost their citizenship because of marriage, to repatriate as naturalized (not birthright) citizens. A wife's nationality depended on residence and her husband's eligibility to naturalize; if she lived abroad, her nationality on re-entry to U.S. territory was therefore subject to the restrictions of the Quota Act. However, because the Cable Act was worded to specifically state that "women citizens" who married ineligible foreigners lost their nationality, it did not apply to American Samoan women, as they were non-citizen nationals.

Under the terms of the 1924 act, also known as the Asian Exclusion Act, Asians were not allowed to enter the country and were excluded from naturalization. It stated that an American-born woman whose nationality was lost because of marriage, regardless of whether that marriage had terminated, was ineligible for naturalization and was considered to have been "born in the country of which [they were] a citizen or subject". The Supreme Court ruling of 1923, in United States v. Bhagat Singh Thind, retroactively removed the nationality of Asian men, automatically revoking their wives' nationality. If a U.S. woman married to a man of Asian descent left the country, she could not be readmitted to the United States. Husbands could petition for an exception allowing their foreign-born wives to lawfully immigrate, but wives were unable to petition for their husbands. Immediately after passage of the 1924 Act, the Department of Labor Secretary, James Davis, recommended extending its provisions to immigrants from Mexico and other countries in the Americas. Every year from 1926 to 1930, Congress considered bills evaluating imposing quotas for immigration from the other nations in the western hemisphere. In June 1924, the Indian Citizenship Act granted Native Americans, unilaterally, nationality in the United States.