Visas are not required for stays up to 28 days for tourism and business travel, however, a valid passport is required with at least 1 blank visa page.  Swift recommends having at least 6 months validity remaining on your passport at all times to travel.  Below are the travel requirements per the US Department of State, please cross-reference this website for any recent changes and more detailed information.

US citizens must have a valid US passport to enter Barbados. No visa is needed to enter Barbados for stays up to 28 days. All US citizens traveling outside of the United States are required to present a passport or other valid travel document to enter the United States. This extended to all sea travel (except closed-loop cruises), including ferry service on June 1, 2009. Travelers must now present a Western Hemisphere Travel Initiative (WHTI) compliant document such as a passport or a passport card for entry to the United States. While passport cards and enhanced driver’s licenses are sufficient for entry into the United States, they may not be accepted by the particular country you plan to visit; please be sure to check with your cruise line and countries of destination for any foreign entry requirements. We strongly encourage all US. citizen travelers to apply for a U.S. passport or passport card well in advance of anticipated travel.

NOTE: Be aware that Caribbean cruises that begin and end in the US (closed loop cruises) do not require that you travel with a valid passport. However, should you need to disembark due to an emergency and you do not have a valid passport, you may encounter difficulties entering or remaining in a foreign country. You may also have difficulty attempting to re-enter the United States by air because many airlines will require a valid passport before allowing you to board the aircraft. As such, we strongly recommend that you always travel abroad with your valid passport.