U.S. Customs and Border Protection (CBP) has published a new, informative background online publication about the Western Hemisphere Travel Initiative (WHTI). This initiative is a joint plan between the Department of State and the Department of Homeland Security to require all travelers (both U.S. citizens and foreign nationals) to show a passport or other acceptable document that defines their citizenship status when entering the U.S.
The WHTI requirements for air travel went into place on January 2007. All U.S. citizens and nonimmigrant foreigners are required to show a valid passport or proof of citizenship when leaving or entering the U.S. from within the Western Hemisphere at an airport of entry. The program was implemented in 2009 for entry into the U.S. by land and sea.