Nationality may be acquired through birth, acknowledgement, naturalization, and reinstatement of nationality, etc., and Koreans with a foreign nationality who meet certain conditions may apply for permission for reinstatement of nationality.
A person who has had the nationalities of both of the Republic of Korea and a foreign country by birth or by dint of the 「Nationality Act」 before he reaches his full twenty years of age shall select one nationality before he reaches his full twenty-two years of age; and a person who becomes a dual national after he reaches his full twenty years of age shall select one nationality within two years from then: Provided that anyone who is enlisted in the first military service shall choose one nationality within 3 months from the time when he is enlisted in the first military service or within 2 years from the time when a reason for military service has lapsed (① when he has completed his active military service, full-time reserve service or recruit service, or is deemed to have completed it; ② when he is subjected to a disposition taken to exempt him from the military service; and ③ when he is enlisted in the second military service).
A national of the Republic of Korea who has voluntarily acquired the nationality of a foreign country shall lose nationality of the Republic of Korea at the time of acquisition of the foreign nationality. A person who has lost nationality of the Republic of Korea (except persons who have reported the abandonment of nationality) shall report the loss of nationality.
Adjudication of nationality is a means to determine whether a person whose acquisition or holding of nationality of the Republic of Korea is unclear is an ROK national upon his formal application therefor. The applicant’s family lines, reasons for emigration, acquisition of a foreign nationality, etc. are examined to determine whether the applicant currently holds nationality of the Republic of Korea.