No. U.S. citizens do not need a passport to travel between the U.S. mainland and Puerto Rico, because Puerto Rico is a U.S. territory and the trip counts as domestic travel, according to USAGov. The same applies to Guam, the Northern Mariana Islands, and the U.S. Virgin Islands.
You still need ID to fly: adults 18 and older must show a REAL ID-compliant driver’s license or another TSA-accepted ID, such as a U.S. passport or passport card. A passport is needed if your itinerary passes through a foreign country, and it is required for American Samoa (or a certified birth certificate) and for Palau, the Marshall Islands, and Micronesia.
Source: USAGov, “Do you need a passport to travel to or from U.S. territories or Freely Associated States?” (updated March 31, 2026). See also TSA, “Acceptable Identification at the TSA Checkpoint”.
Image: A street corner in Old San Juan, Puerto Rico, photo by P. Hughes (CC BY-SA 4.0), via Wikimedia Commons.