Unfortunately, there is no unified Romanization system. Several rules for Korean Romanization have been developed and used by different groups. Here is a quick overview of the main ones.
- The Revised Romanization of Korean is the most commonly used and widely accepted system of romanization for Korean. It includes rules both for transcription and transliteration. It was approved in 2000 and has been officially used in South Korea now since then. Road signs and textbooks are required to follow these rules. Almost all road signs, names of railway and subway stations have been changed to follow this system. Romanization of surnames and existing companies' names has been left untouched; however, the government encourages using the new system for given names and new companies.
- The McCune–Reischauer appeared around 1937. It was the first transcription to gain some acceptance. A slightly modified version of this set of rules was the official system for Korean in South Korea from 1984 to 2000, and another modification of the same system is still the official one in North Korea. MR uses diacritical marks to indicate orthographic syllable boundaries in cases that would otherwise be ambiguous.
- The ALA/LC Romanization rules are the standard for Korean Romanization used by American libraries, including ULS. These are based on the McCune-Reischauer system but deviate from it.
- The Korean Yale Romanization was developed in 1942 at Yale University for Romanizing the four East Asian languages: Mandarin, Cantonese, Korean, and Japanese. This system is mainly used by linguists. In this system, vowel length in old or dialectal pronunciation is indicated by a diacritical mark. In cases that would otherwise be ambiguous, orthographic syllable boundaries are indicated with a period. It also indicates disappearance of consonants.
There are also other systems, not very widely spread, for instance, the Lukoff romanization, developed 1945–47 for his Spoken Korean coursebooks.
The McCune–Reischauer-based systems and the Revised Romanization differ from each other mainly in the choice of how to represent certain hangul letters. Both systems 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. Therefore, 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 or letters, regardless of the context, thus not indicating the hangul letters' context-specific pronunciation.
Even in texts that claim to follow one of the above-mentioned systems, variations and changes are common, which can present a major obstacle. For example, when conducting an automated search on the Internet, the searcher must check all possible spelling variants, which can be time-consuming.
In addition to these systems, many people spell names or other words in a random manner, producing more variations.