One of the many functions which diplomatic and consular officials have to perform is the issuing of passports. Passports are documents of identity which are issued in the name of the head of the state in favour of persons who wish to travel or sojourn in foreign countries. They contain a request to all persons who may be concerned to afford assistance and protection which the holder of the passport may stand in need. In modern times, possession of a passport has become an absolute necessity in foreign travel, though less than a hundred years ago only a few countries, such as Persia, Roumania, Russia and Serbia, required passports from aliens entering their territory and none required passports from departing aliens. The two world wars and the development of modern means of fast travel have, however, led to greater control by many states, which is done by means of passports and visas. In addition to enabling its holder to leave his country and enter a foreign state, a passport implicitly confers upon the traveller the right to return to his own country.