Passport to Your National Parks is a program through which ink stamps can be acquired at no cost at park visitor centers and ranger stations at nearly all of the 431 units of the United States National Park System and most of the National Park Service's affiliated areas. The program is run by Eastern National, a non-profit organization that operates bookstores in many park locations.
The ink stamps applied with a rubber stamp are similar in nature to passport stamps stamped in a traveler's national passport and serve as a record of each park visit. Eastern National has described the stamps as cancellations, but this is incorrect as a cancellation is a mark that cancels the validity of a postage stamp, while these mark a record of visitation like a passport stamp and denote a place and date like a postmark and do not cancel anything. Collectors of the stamps have formed a non-profit social club, the National Park Travelers Club, a group which holds annual conventions.