The U.S. government does not require passports when traveling directly to and returning from any of the U.S. territories, including the U.S. Virgin Islands, Guam, American Samoa and the Northern Mariana Islands.
If you're taking a Caribbean cruise with a port in Puerto Rico as well as foreign ports, you will not need a passport, but only if it is a closed-loop cruise.
Puerto Rico is considered part of the United States. A passport will be required if you travel to any foreign territory and return to Puerto Rico.
U.S. citizens traveling directly between the U.S. and its territories need only proper photo identification, such as a valid state-issued driver's license or ID card, valid passport or government-issued ID.
Because U.S. citizens don't need a passport to go to Puerto Rico, many Americans are choosing to escape the winter months, December to April. Expect to pay higher prices during that time.
