Passport

a formal document or certification issued by a national government identifying a traveler as a citizen or national with a right to protection while abroad and a right to return to the country of citizenship. 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 countries is a development of the 19th and 20th centuries. A passport is a small booklet containing a description of the bearer and an accompanying photograph that can be used for purposes of identification. Most countries require travelers entering their borders to obtain a visa—i.e., an endorsement made on a passport by the proper authorities denoting that it has been examined and that the bearer may proceed. The visa permits the traveler to remain in a country for a specified period of time. By the late 20th century the demands of tourism had prompted countries in western Europe to relax their travel regulations so that travelers could enter them without visas or, in some cases, even without passports.

In the United States, upon application, passports are issued to U.S. citizens by the Department of State and its 12 passport agents in various cities; by the clerks of federal and certain state courts; by certain designated post offices; and by U.S. consular authorities abroad. The passport is required for both departure and reentry to the United States. It is valid for 10 years for adults but for only 5 years for persons age 15 or younger. A U.S. passport cannot simply be renewed but rather must be completely replaced when it expires.
In the United Kingdom, the Passport Agency within the Home Office issues passports at offices in several major cities. Passports are issued to citizens of the United Kingdom and its colonies but not to citizens of Commonwealth countries. British passports are valid for 10 years for adults and for 5 years for persons under age 16.