McCune–Reischauer

It was created in 1937 and the ALA-LC variant based on it is currently used for standard romanization library catalogs in North America.

[5] South Korea formerly used another variant of McCune–Reischauer as its official system between 1984 and 2000, but replaced it with the Revised Romanization of Korean in 2000.

The apostrophe is also used to distinguish ㄴㄱ from ㅇㅇ: 연구 is transcribed as yŏn'gu while 영어 is yŏngŏ.

The breve is used to differentiate vowels in Korean: ㅜ is spelled u, ㅡ is ŭ, ㅗ is o and ㅓ is ŏ.

Because of the dual use of apostrophes—the more common being for syllabic boundaries—it can be ambiguous for persons unfamiliar with McCune–Reischauer as to how a romanized Korean word is pronounced.

In the early days of the Internet, the apostrophe and breve were even omitted altogether for both technical and practical reasons, which made it impossible to differentiate the aspirated consonants k', t', p' and ch' from the unaspirated consonants k, t, p and ch, ㄴㄱ (n'g) from ㅇㅇ (ng), and the vowels ㅜ and ㅡ as well as ㅗ from ㅓ.

As a result, the South Korean government adopted a revised system of romanization in 2000.

[6] However, Korean critics claimed that the Revised System fails to represent ㅓ and ㅡ in a way that is easily recognizable and misrepresents the way that the unaspirated consonants are actually pronounced.

Irregularities occurring in proper names such as in P'yŏngyang 平壤 which is colloquially pronounced P'iyang or P'eyang, should usually be ignored in romanizations intended for scholarly use.