The Western Hemisphere Travel Initiative (WHTI) went into effect in 2007, changing the requirements for crossing the U.S.-Canadian border by air. While passports are generally required to cross a border, other documents are acceptable by land.
You must have proof of citizenship and proof of identity to cross into Canada from the United States. U.S. citizens may use a passport, a passport card, a NEXUS card, a government-issued photo ID or proof of citizenship to enter Canada.
To enter the United States from Canada by air, a U.S. citizen must have a valid U.S. passport -- a passport card will not be accepted. To enter the United States from Canada by land or sea, any WHTI-compliant document will be accepted. Such documents include passports, passport cards, NEXUS cards and enhanced drivers' licenses. NEXUS cards, designed for frequent travelers, allow expedited border crossings.
U.S. citizens under the age of 16 do not need passports and must only present proof of citizenship to cross from the United States into Canada. Minors aged 16 and under only need to present a birth or naturalization certificate to cross from Canada into the United States; if traveling with a youth group such as a school or church, the age limit is raised to 19.
