U.S and Canadian Citizens must bring a government-issued photo I.D and proof of citizenship (U.S birth certificate or naturalization certificate) or a passport for re-entry into the United States. Children ages 18 and under only require a birth certificate.
Non-U.S. Citizens should bring either a Passport, I-94, Multiple Entry Visa, or Resident Alien Card for re-entry into the United States.
The Department of Homeland Security will requires passports from US citizens crossing the Mexican and Canadian borders by land or sea as of June 1, 2009.
We encourage you to check with immigration services for official updates.