Currently U.S. persons are exempt from carrying passports when returning from Canada, Mexico, and the Caribbean. Current U.S. Passport Requirements and Costs2

On January 31, 2008, the Department of Homeland Security again tightened travel regulations with border states by requiring that all U.S. and Canadian citizens, 19 or older, present both a government-issued proof of identity (such as a driver's license) and proof of citizenship (such as a birth certificate) to cross a border by land or sea into the United States. For Americans and Canadians under the age of 18, only proof of citizenship (such as a birth certificate) is necessary. Since January 23, 2007, all people, including children, traveling by air between the United States and Canada, Mexico, Bermuda, and the Caribbean have been required to present a passport or other valid travel document to enter the United States. Most Recent Passport Requirement Changes

The Department of State fully implemented the final phase of passport requirements for travelers entering the United States by land and sea on June 1, 2009. U.S. or Canadian children under the age of 16, however, are allowed to present an original or copy of their birth certificate or other proof of citizenship. Groups of U.S. or Canadian children under the age of 19, when traveling in church, school, or social groups, or sports teams, and when entering under adult supervision, also can present birth certificates or other proof of citizenship, rather than a passport. Prior to 2007, standard passport wait times had been four to six weeks, but this lengthened to three or four months that year from the time of application to receipt of the passport.
Prior to 2007, little or no documentation was required to enter the United States from Canada, Mexico, Bermuda, or the Caribbean. In December 2004, with the 9/11 Commission recommending tighter borders to help prevent another terrorist attack, Congress passed the Western Hemisphere Travel Initiative (WHTI), which now requires passports for anyone entering the United States. As of mid-2009, approximately 30% of American citizens hold a passport.
After the January 2007 implementation of phase I of the new passport regulations (requiring passports when entering by air ), the Department of State was deluged with passport applications. The time necessary to get a passport expanded from the typical four to six weeks to several months, ruining many Americans' travel plans.
On January 31, 2008, another change occurred. Government-issued proof of identity and citizenship documents are required to enter the United States from Canada, Mexico, Bermuda, and the Caribbean, according to the Department of Homeland Security. People under the age of 18, however, are allowed to present only proof of citizenship, such as a birth certificate.
Phase II, implemented on June 1, 2009, adds to the existing requirements that travelers have passports for all land and sea crossings. U.S. or Canadian children under the age of 16, however, are allowed to present an original or copy of their birth certificate or other proof of citizenship. Groups of U.S. or Canadian children under the age of 19, when traveling in church or school groups, social groups, or sports teams, and when entering under adult supervision, also can present birth certificates or other proof of citizenship, rather than a passport. This report will be updated as events warrant.