United States immigration policy, which regulates entry and citizenship, is primarily overseen by Congress and enforced by the Department of Homeland Security (DHS) since 2003. Historically, the nation transitioned from a period of largely open immigration in the early 19th century to increasingly strict policies by the late 19th and early 20th centuries. While the 1868 Fourteenth Amendment established birthright citizenship, early federal laws like the Naturalization Act of 1790 restricted naturalization to white immigrants, later expanding to African Americans in 1870 but explicitly banning Chinese immigration with the 1882 Chinese Exclusion Act.
The DHS carries out policy through agencies such as Customs and Border Protection (border control), Immigration and Customs Enforcement (illegal immigration), and Citizenship and Immigration Services (legal immigration and naturalization). These policies, developed through various Naturalization and Immigration Acts and significant Supreme Court rulings like United States v. Wong Kim Ark (1898) which affirmed birthright citizenship for children of immigrants, reflect a complex and often shifting approach to national identity and demographics.