United States and Canadian citizens can stay in the Bahamas for up to six months without a visa, but you must have your return or onward ticket before entering.
Regardless of age, all travelers need a passport valid for at least six months to travel to the Bahamas.
As of June 1, 2009, United States citizens must have a valid passport to enter the Bahamas by sea. On a closed loop cruise (a cruise that begins and ends at the same port), you are not required to have a passport, but you may not be allowed to disembark from the ship.
A passport card is a new alternative for those traveling by land or sea within the United States, Canada, the Caribbean and Bermuda. It is less expensive, but it will not work for international travel.
Be aware that visa requirements may be different depending on your country of origin and length of stay, and requirements are always subject to change.