"This rule finalizes the proposed rule published on October 17, 2006, and implements certain provisions of Section 7209 of the Intelligence Reform and Terrorism Prevention Act of 2004 (IRTPA). The IRTPA provides that United States citizens and non-immigrant aliens may enter the United States only with passports or such alternative documents as the Secretary of Homeland Security may designate as satisfactorily establishing identity and citizenship. The statute requires that the Secretary of Homeland Security, in consultation with the Secretary of State, develop and implement a plan to require virtually all travelers entering the United States to present a passport or other document or combination of documents that are deemed by the Secretary of Homeland Security to be sufficient to denote identity and citizenship."
U.S. Dept. of State: http://www.state.gov/
Federal Register (December 31, 2007), v.72 no.249, p. 74169-74173