It's small enough to fit in a pocket, but a passport is packed full of information – and part of becoming an informed world traveler is understanding the anatomy of this all-important document. Most of the important stuff is found near the front on the photo page. As you travel to other countries, the other pages fill up with stamps that customs agents use to mark your entry. Each country issues its own passport, but the standard American version is always the same.

Page One: Message From the Secretary of State

The first page of a standard American passport includes a quote by Abraham Lincoln, an image of the seal of the United States, and a message from the office of the Secretary of State asking authorities of other nations to allow the passport holder access. The message is repeated in French and Spanish. This isn't a page that you'll need to use or refer to at any point during your travels.

Page Two and Three: The Important Information

Flip the first page to reach the most critical part of a passport: the photo page. In your own passport, on this page, you'll see your photo, a heading that reads "United States of America" and several lines of typed information. At the top, a letter designates what type of passport it is; most people have a standard type P version. Next to that is a country code (USA, in this case) and the passport's unique document number.

Below that are lines for the holder's last name, first and middle name, nationality, date of birth, place of birth, the date the passport was issued, the date it expires, the holder's gender, and the authority that issued the passport – the United States of America. That's all information that the Department of State gathered from your application and the supporting documentation you provided along with the application. Page two is one of only two places in your passport where you'll see printed information specific to you; the other is the inside back cover, where the passport number is printed. All other pages should look the same as those of any other standard American passport.

Page three displays the preamble of the Constitution and has a line for the signature of the passport holder. Sign that line if you haven't already. Before approaching a customs agent, open the passport to this page to make the agent's job a little easier.

Pages Four Through 28: Everything Else

The fourth page of a passport provides lines for the holder to write in an address and phone number in the event that the document is lost, followed by three pages of general information about how to care for a passport and stay safe abroad.

Pages eight through 27, called visa pages, are mostly empty except for quotes from important American figures. When you arrive at customs of a foreign country, an agent will check the photo page to make sure it's valid and belongs to you, then flip to a visa page and press down a stamp that denotes the country and the date of entry. Some countries also use exit stamps to mark your departure.

Check the passport requirements for every country on your itinerary, especially if these pages are mostly filled up. Customs agents in some countries will stamp a page that's already half full. In other places, the requirements are stricter. To visit South Africa, for example, your passport must have two consecutive blank visa pages.