Persons born in Korea are given a unique Resident Registration Number at birth. This number is a national identifier and is shown on the Resident Identity Card that Koreans must carry at all times beginning at age 18, on Korean passports and on military identifications. It also becomes the National Pension Number when a person begins to work.

Foreign nationals living in Korea for three months or longer are issued a Foreigner Registration Number. Korea uses this number as the person's National Pension Number

The number consists of 13 digits. The first six digits are the date of birth in year, month, day order. The seventh digit identifies the sex of the person; a male is 1 and a female is 2. Digits eight through 12 indicate the region of Korea in which the person was born. The final digit is a “check digit” that mathematically confirms the validity of the preceding 12 digits.

For foreign nationals, digits eight through thirteen identify the year of registration and the Registration Office.