The first clause of the Fourteenth Amendment to the U.S. Constitution, known as the Citizenship Clause, provides that [a]ll persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. This generally has been taken to mean that any person born in the United States automatically gains U.S. citizenship, regardless of the citizenship or immigration status of the person’s parents, with limited exceptions such as children born to recognized foreign diplomats. The current rule is often called birthright citizenship. However, driven in part by concerns about unauthorized immigration, some have questioned this understanding of the Citizenship Clause, and in particular the meaning of subject to the jurisdiction [of the United States]. This book traces the history of birthright citizenship under U.S. law and discusses some of the legislation in recent Congresses intended to alter it.