Starting June 1, 2009, travelers entering the US through land or sea ports must possess an approved travel document to enter the US. Under the Western Hemisphere Travel Initiative (WHTI), all travelers entering the US after June 1st, including US citizens and Canadian citizens, must provide one of the following documents:
1. US or Canadian passport;
2. Trusted Traveler Card (NEXUS, SENTRI or FAST);
3. US Passport Card;
4. State or province-issued enhanced drivers license (where available);
5. Form I-872 American Indian Card or enhanced tribal card;
6. Military Identification Card of a member of the US Armed Forces traveling under orders; and
7. US Merchant Mariner Document (for US citizens conducting official maritime business).
Travelers under 16-years-old only need to show a birth certificate or alternative evidence of citizenship.
Legal permanent residents (LPRs) of the US should present evidence of such status, such as the Alien Registration Card (I-551). LPRs do not need a US passport.
The WHTI is a joint plan between the Department of Homeland Security and the US Department of State that determines the documentation requirements the entry of people into the US. It implements the recommendations of the 9/11 Commission and Congress.