Alien registration (外国人登録, gaikokujin tōroku) is a system used to record information regarding aliens resident in Japan. Under Japanese law, foreign residents who work, study, or stay in Japan for more then 90 days (with exception to diplomats and military personnel under a status of forces agreement.^[1]) are issued a "Residence Card" (在留カード, zairyū kādo) at a point of entry by Japanese immigration officers. Their immigration information is then submitted to the Ministry of Justice.

Foreign residents are required to carry their resident card at them at all time, as well as submit a residence record (jūminhyō, 住民票) to the municipality they reside in. If a foreign resident leaves Japan, they must return their resident card before their departure at an airport, seaport, or the nearest Ministry of Justice office.^[2]

Some Korean residents of Japan have a Special Permanent Resident Certificate instead of a Residence Card.

The information stored in the alien registration system included:

• Date of registration
• Name (including any legal alias)
• Date of birth
• Gender
• Nationality and place of residence in home country
• Place of birth
• Employer/school, work/school address and occupation (if any)
• Passport number and date of issuance
• Date of landing in Japan
• Status of residence and duration of stay
• Residential address
• Information regarding household members (including name, date of birth, nationality and relationship)
• Information regarding parent(s) and/or spouse residing in Japan.

This information was recorded in a physical document called a tōroku genpyō (登録原票), kept by the municipality in which the subject lived. Any changes in registered information had to be reported to the municipal office.^[3]

If a resident alien moved within Japan, they were required to report their move to the new municipality of residence,

Registered aliens are allowed to adopt an alias (通称名, tsūshōmei) or 通名 as a second legal name. This resembles the 通称 that Japanese are allowed to use — for example, to continue using a maiden name at work and on bank accounts after marriage. Foreigners who are long-term residents of Japan, particularly ethnic Koreans whose families have lived in Japan for generations, often adopt Japanese names as aliases in order to integrate within society. Ethnic Japanese who live in Japan as resident aliens may use a legal alias to reflect their ancestral name. Legal aliases are also used when registering a seal in a different script than the applicant's legal name (e.g., in katakana rather than Latin script).

Japanese nationals often use aliases for non-official purposes. For example, women often continue to use their maiden names following marriage, even though they are required to adopt the same family name as their husband for their legal name. However, Japanese nationals are not permitted to use an alias for legal purposes: their name on any official document (e.g. domestic use Japanese identification) must match the name appearing in their family register and resident register. Japanese passports may contain alternate names in parentheses next to the family name or the given name if the Japanese can show a legal connection and use of these names overseas. Multiple alternate names are separated by slashes. Non-standard non-Hepburn romanization may also be used for the main names if one can show a legal connection using these spellings.^[4]

• Guide for Foreign Residents in Japan (not yet updated for new system)
• Registration of a Japanese name alias explained in Japanese by Nishio City, Aichi Prefecture
• About.com article in Japanese on aliases (17 Oct 2006) (in Japanese)