Many romanization schemes are in common use:
- Revised Romanization of Korean (RR, also called South Korean or Ministry of Culture (MC) 2000): This is the most commonly used and widely accepted system of romanization for Korean. It includes rules both for transcription and for transliteration. South Korea now officially uses this system which was approved in 2000. Road signs and textbooks were required to follow these rules as soon as possible, at a cost estimated by the government to be at least US$20 million. Almost all road signs, names of railway and subway stations on line maps and signs etc. have been changed. Romanization of surnames and existing companies' names has been left untouched; the government encourages using the new system for given names and new companies.
- RR is similar to MR, but uses neither diacritics nor apostrophes, which has helped it to gain widespread acceptance on the Internet. In cases of ambiguity, orthographic syllable boundaries may be indicated with a hyphen, although state institutions never seemed to make use of this option until recently. Hyphenation on street and address signs is used to separate proper names and numbers from their assigned function. As of 2014, under mandate from the Roadname Address Act, Korea Post officially changed the older address system from lot-based district subdivisions to a street-based system that regularly utilizes hyphenation in order to disambiguate. The Ministry of the Interior also provided the public with various service announcements and websites forewarning of the change toward a clear and complete signage system classifying all streets and individual addresses with romanization (of which hyphenation is a systematic part).
- McCune–Reischauer (MR; 1937?), the first transcription to gain some acceptance. A slightly modified version of MR was the official system for Korean in South Korea from 1984 to 2000, and yet a different modification is still the official system in North Korea. MR uses breves, apostrophes and diereses, the latter two indicating orthographic syllable boundaries in cases that would otherwise be ambiguous.
- Several variants of MR, often also called "McCune's and Reischauer's", differ from the original mostly in whether word endings are separated from the stem by a space, by a hyphen or not at all; and if a hyphen or space is used, whether sound change is reflected in a stem's last and an ending's first consonant letter (e.g. pur-i vs. pul-i). Although mostly irrelevant when transcribing uninflected words, these variants are so widespread that any mention of "McCune–Reischauer romanization" may not necessarily refer to the original system as published in the 1930s. MR-based romanizations have been common in popular literature until 2000.
- The ALA-LC / U.S. Library of Congress system is based on but deviates from MR. Unlike in MR, it addresses word division in seven pages of detail. Syllables of given names are always separated with a hyphen, which is expressly never done by MR. Sound changes are ignored more often than in MR. ALA-LC also distinguishes between ‘ and ’.
- Yale (1942): This system has become the established standard romanization for Korean among linguists. Vowel length in old or dialectal pronunciation is indicated by a macron. In cases that would otherwise be ambiguous, orthographic syllable boundaries are indicated with a period. Indicates disappearance of consonants.
- Lukoff romanization, developed 1945–47 for his Spoken Korean coursebooks
- Romanization of Korean: Chosŏn Sahoe Kwahagwŏn (Hangul: 조선민주주의인민공화국사회과학원, Hanja: 朝鮮民主主義人民共和國社會科學院) romanization
McCune–Reischauer-based transcriptions and the Revised Romanization differ from each other mainly in the choice of how to represent certain hangul letters. Both attempt to match a word's spelling to how it would be written if it were an English word, so that an English speaker would come as close as possible to its Korean pronunciation by pronouncing it naturally. Hence, the same hangul letter may be represented by different Roman letters, depending on its pronunciation in context. The Yale system, on the other hand, represents each Korean letter by always the same Roman letter(s) context-independently, thus not indicating the hangul letters' context-specific pronunciation.
Even in texts that claim to follow one of the above, aberrations are a common occurrence and a major obstacle, e.g. when conducting an automated search on the Internet, as the searcher must check all possible spelling variants, a considerable list even without such aberrations.
In addition to these systems, many people spell names or other words in an ad hoc manner, producing more variations (e.g. 이/리 (李), which is variously romanized as Lee, Yi, I, or Rhee). For more details, see Wikipedia:Naming conventions (Korean).
SKATS is a transliteration system that does not attempt to use letters of a similar function in Western languages. A similar approach is to transliterate by hitting the keys that would produce a Korean word on a keyboard with 2[du]-beolsik layout. This can often be seen on the internet, for example in usernames.