A U.S. passport book is the traditional travel document that allows the holder to enter and exit the United States and foreign countries by air or sea. It contains a significant number of pages for visas and entry/exit stamps. A U.S. passport card, on the other hand, is a smaller, wallet-sized document that can only be used for land and sea travel between the United States, Canada, Mexico, and the Caribbean region. It does not have as many pages as a passport book and is not valid for air travel.