"Naturalization is the process by which U.S. citizenship is conferred upon a foreign citizen or national after he or she fulfills the requirements established by Congress in the Immigration and Nationality Act. After naturalization, foreign-born citizens enjoy the same benefits, rights and responsibilities that the Constitution gives to native born U.S. citizens, such as the right to vote. They can also apply for a U.S. passport to travel overseas and receive U.S. government protection and assistance when abroad. This Office of Immigration Statistics Annual Flow Report presents information on the number and characteristics of foreign nationals aged 18 years and over who were naturalized during 2006."
United States. Dept. of Homeland Security: http://www.dhs.gov