Air Travel

ALL PERSONS traveling by air outside of the United States are required to present a passport book or other valid travel document to enter or re-enter the United States.

Land and Sea Travel

ALL PERSONS traveling by land and sea outside of the United States are required to present a passport book/card, or other valid travel documents to enter or re-enter the United States.

The following summarizes information available on the Department of Homeland Security’s website:

Effective June 1, 2009, all U.S. citizens are now required to present a passport book, passport card, or WHTI-compliant document when entering the United States.

Please Note: Children under age 16 will be able to continue crossing land and sea borders using only a U.S. birth certificate (or other form of U.S. citizenship such as a naturalization certificate.). The original birth certificate or a copy may be used. See the Department of Homeland Security's Ready, Set.. Go! for more information on the changing travel requirements. 

The passport requirement does NOT apply to U.S. citizens traveling to or returning directly from a U.S. territory.

U.S.PASSPORT AND WHTI COMPLIANT DOCUMENTS:

U.S. Passport: U.S. citizens may present a valid U.S. passport when traveling via air, land or sea.
The Passport Card: The passport card is only valid for land and sea travel between the U.S. and Canada, Mexico, the Caribbean region, and Bermuda. 

WHTI-Compliant Travel Documents for U.S. citizen travel via land and sea, as of January 31, 2008:
 

• Trusted Traveler Cards (NEXUS, SENTRI, or FAST)
• State Issued Enhanced Driver’s License (when available)
• Enhanced Tribal Cards (when available)
• U.S. Military Identification with Military Travel Orders
• U.S. Merchant Mariner Document when traveling in conjunction with official maritime business
• Native American Tribal Photo Identification Card
• Form I-872 American Indian Card

For further information see U.S. Customs and Border protection.