Over the last decade or so, concern about the level of immigration, focused particularly on illegal immigration, has sporadically led to a re-examination of a long-established tenet of U.S. citizenship, codified in the Fourteenth Amendment of the U.S. Constitution and Section 301(a) of the Immigration and Nationality Act [INA] (8 U.S.C. Section 1401(a)), that a person who is born in the United States, subject to its jurisdiction, is a citizen of the United States regardless of the race, ethnicity, or alienage of the parents. The war on terror and the case of Yaser Esam Hamdi, a U.S.-Saudi dual national captured in Afghanistan fighting with Taliban forces, further heightened attention and interest in restricting automatic birthright citizenship, after the revelation that Hamdi was a U.S. citizen by birth in Louisiana to parents who were Saudi nationals in the United States on non-immigrant work visas and arguably entitled to rights not available to foreign enemy combatants. This report traces the history of this principle under U.S. law and discusses some of the legislation in recent Congresses intended to alter it. The traditional English common-law followed the doctrine of jus soli, under which persons born within the dominions of and with allegiance to the English sovereign were subjects of the sovereign regardless of the alienage status of their parents. The exceptions to this rule are persons born to diplomats, who are born subjects of the sovereign whom the parents represent abroad, and persons born to citizens of a hostile occupying force, who are born subjects of the invading sovereign. Although the states and courts in the United States apparently adopted the jus soli doctrine, there still was confusion about whether persons born in the United States to alien parents were U.S. citizens. This arose because citizenship by birth in the United States was not defined in the Constitution nor in the federal statutes. Legal scholars and law makers were torn between a "consensualist" doctrine of citizenship, by which a person and a government consent to be mutually obligated, and an "ascriptive" doctrine by which a person is ascribed citizenship by virtue of circumstances beyond his control, such as birth within a particular territory or birth to parents with a particular citizenship. Additionally, African-Americans were not considered citizens of the United States, even if they were free. Native Americans also were not considered U.S. citizens because they were members of dependent sovereign Indian nations. The Civil Rights Act of 1866 and the Fourteenth Amendment, ratified in 1868, extended birthright citizenship to African-Americans, but the United States Supreme Court made clear that although U.S.-born children of aliens were U.S. citizens regardless of the alienage and national origin of their parents, Native Americans still were not U.S. citizens under the terms of those laws. Native Americans were made U.S. citizens by statute. In recent Congresses there have been several legislative proposals to amend the Constitution and the Immigration and Nationality Act to limit automatic citizenship upon birth in the United States so that persons born in the United States to parents who are unlawfully present in the United States or are non-immigrant aliens would not become U.S. citizens, e.g., H.J.Res. 41, H.J.Res. 46, and H.R. 698 in the 109th Congress. This report will be updated as necessary.