U.S. Citizen need passport.
Every U.S. citizen — including infants — needs a valid passport in his or her own name to travel overseas.
Beginning January 23, 2007, ALL persons, including U.S. citizens, traveling by air between the United States and Canada, Mexico, Central and South America, the Caribbean, and Bermuda will be required to present a valid passport.
Link to get Passport for US Citizens
The Passport Services Office provides information and services to American citizens about who to obtain, replace or change a passport.A passport is an internationally recognized travel document that verifies the identity and nationality of the bearer.
A valid U.S. passport is required to enter and leave most foreign countries. Only the U.S. Department of State has the authority to grant, issue or verify United States passports.
To get information and your US Passport enter here:
US Department of State