If you've ever traveled outside the United States, one of the most important tasks you had to complete before your trip was applying for a passport. A copy of your original birth certificate used to suffice for short trips to Mexico or the Caribbean, say on a cruise. But, generally speaking, if you want to see the world, you have to have a passport -- the only universally accepted form of identification.

Photo courtesy of the U.S. State Department The new U.S. e-passport

In this article, you'll find out when and why you need a passport and how to apply for one.

What Exactly is a Passport and How Long Have They Been Around?

Passports have been around in some form for hundreds of years. Governments learned long ago that an official document or certification -- one that identified a traveler as a citizen or national with a right to protection while abroad and a right to return to the country of his citizenship -- is a necessity. Passports, letters of transit and similar documents were used for centuries to allow individuals to travel safely in foreign lands, but the adoption of the passport by all nations was a development of the 19th and 20th centuries. According to State Department historians, except for brief periods during wartime, passports were not generally required for travel abroad and few obstacles were presented by foreign states' passport requirements until after 1914. An executive order on Dec. 15, 1915, required every person entering or leaving the United States to have a valid passport.

In the United States, passports are issued upon application to U.S. citizens by the State Department and its 14 passport agencies in major cities (including Boston, Miami, Los Angeles and Houston), by the clerks of federal and certain state courts, certain designated post offices and by U.S. consular authorities abroad. The passport is required for both departure from and re-entry to the United States. It is valid for 10 years for adults and five years for people under 18 (their appearances generally change more often and more significantly, so more photo updates are needed). A U.S. passport cannot simply be renewed but must be completely replaced when it expires.

Photo courtesy of the U.S. State Department The photo page of the e-passport

U.S. passports are periodically upgraded to incorporate new technologies designed to thwart counterfeiters and forgers. To deter fraud, passport production uses advanced printing technology, special inks and security thread in the paper. The most recent innovation is the RFID (radio frequency identification) passport, or e-passport, which was introduced in August 2006 and has a computer chip embedded in the back cover. The chip contains your biographical information and a digital copy of your photograph, which is used with facial recognition technology for identification purposes. The data can be read only by password-enabled chip-readers at a very close distance (around four inches), and the reinforced back cover ensures that the chip cannot be accessed if the passport is closed.