A passport is a type of document used to provide evidence about the holder's identity, such as their nationality and place of birth, primarily for the purpose of international travel. Passports are usually issued by governments to the citizens of their state. Precisely who is allowed to hold a passport is a matter for a nation's government, rather than being an automatic right, and the document itself is generally the property of the state rather than the holder.
Possession of a passport does not guarantee that the holder will be allowed to enter a foreign country, as governments impose conditions on passport holders which must be satisfied prior to granting access. For example, holders of certain nationalities may be refused entry altogether, depending on the diplomatic relations between countries. The passport itself may provide evidence that allows government representatives or immigration officials to judge whether to allow the holder to enter the country, because the document allows previous instances of entering and exiting a territory to be recorded in the form of official stamps, as well as official 'observations', i.e. extra information about how the passport has been obtained or used.
Often a passport holder is required to obtain a visa prior to or on arrival at the destination country. This consists of one or more official stamps or stickers placed in the passport to indicate to immigration officers that the holder has satisfied various conditions set by the government. These stamps are usually obtained at a foreign embassy or consulate some time before travel, and may be issued or denied for a variety of reasons. A visa in no way guarantees that the passport holder will be granted entry, however.
Passports around the world have changed much over the years, and today often incorporate sophisticated anti-fraud measures to reduce the risk of duplication or tampering. Earlier passports were much simpler documents, often with a photograph simply glued inside, and still earlier passports had, by today's standards, little information to reliably identify the holder. Nor were passports a mandatory travel document until well into the twentieth century.
Today, passports are a common part of international journeying, but in some cases can be left at home: countries in Europe's Schengen Area, for instance, have no internal border controls, so identity documents are typically not required to move between, for example, Spain and Portugal. At the other end of the scale, some countries require that foreign nationals travelling under certain categories of visa carry their passports at all times - as in Japan, for instance, where tourists are committing an offence if found without a passport.