The Soviet passport was an identity document issued pursuant to the laws of the Union of Soviet Socialist Republics (USSR) for citizens of the USSR. For the general purposes of identity certification, Soviet passports contained such data as name, date of birth, gender, place of birth, ethnicity, and citizenship, as well as a photo of the passport holder. At different stages of development of the Soviet passport system, they could also contain information on place of work, social status (marriage, children), and other supporting information needed for those agencies and organizations to which the Soviet citizens used to appeal. The passport system of the Soviet Union underwent a number of transformations in the course of its history. In the late Soviet Union citizens of age sixteen or older had to have an internal passport. In addition, a passport for travel abroad (заграничный паспорт, загранпаспорт, zagranpasport, often confusingly translated as "foreign passport") was required for travel abroad. There were several types of abroad passport: an ordinary one, known simply as "USSR zagranpasport", a civil service passport (служебный паспорт, sluzhebny pasport), a diplomatic passport, and a sailor's passport. Internal passports were serviced by "passport offices" (паспортный стол, pasportny stol) of local offices of the MVDs of Soviet republics. Abroad passports were handled by the Ministry of Foreign Affairs of the corresponding Soviet republic. Internal passports were used in the Soviet Union for identification of persons for various purposes. In particular, passports were used to control and monitor the place of residence by means of propiska. Officially, propiska was introduced for statistical reasons: since in the planned economy of the Soviet Union the distribution of goods and services was centralized, the overall distribution of population was to be monitored. For example, a valid propiska was necessary to receive higher education or be employed.