According to the U.S. Department of State, passports are not required for any U.S. territory. These territories include Guam, the U.S. Virgin Islands, American Somoa, the Marianas and Puerto Rico.
According to the Guam Visitor Bureau, you will need a photo identification and proof of citizenship--such as a birth certificate--to enter Guam. A photo identification needs to be something official like a driver's license or state ID card.
However, the no-passport rule only applies if you are traveling directly to and from a United States territory. A passport will be required for any foreign travel during your trip.
More than a dozen countries have been given Guam-only visa waiver entry. Among them are Australia, New Zealand, Japan, United Kingdom and Republic of Korea.
Citizens from countries not included in the waiver program must have a valid passport along with a United States visa to enter Guam.
