Every U.S. passport book has a unique, 9-digit identifying number, called a passport book number. It can be found in the upper right-hand corner of the second page of the passport.
The number can actually include both numbers and letters, which correspond to information about the passport holder and the passport itself. The first two numbers, for example, show which passport office issued the book.
While it can be helpful to know your passport number, you won’t be able to travel internationally without your physical passport. If your passport has been lost or damaged, you can use Form DS-11 to get a replacement. However, you must apply in person at a passport issuing agency.