Resident Registration Cards (Jumin deungnokjeung), drivers licenses (Unjon Myeonheojeung) and passports (Yogwon) are considered legal identification for Korean citizens in Korea, but Resident Registration Cards are the most common, since they are issued to every Korean national who is at least 17 years old. Resident Registration Cards include a person's name, Resident Registration Number, address and photo.
Resident Registration Numbers are issued to all Korean citizens upon the registration of birth. Each is 13 numbers in length, with the first six being a person's date of birth. A person born on 30 April 1962, therefore would have a Resident Registration Number that begins with 620430. The seven numbers that follow are particular to that individual. The first of these seven numbers indicates gender. For persons born in the 20th century, the first number of these seven is 1 for males and 2 for females. This means you can tell a person's age and gender just by looking at his or her Resident Registration Number.
Foreigners residing in Korea do not have Resident Registration Cards, so use passports or Alien Registration Cards. Since it proves that you are a legal resident, you will need your Alien Registration Card for many common everyday needs while living in Korea, for example when you open a bank account, apply for health insurance or a Korean driver's license, find employment, sign a housing contract or in various other situations.