McCune-ReischauerMcCune-Reischauer is a romanization system of the Korean language, created in 1937 by two Americansns: George M. McCune and Edwin O. Reischauer. It does not adhere to Hangul but is relatively phonetic. North Korea and many Western countries use this system while South Korea replaced it with a new romanization system that was created by the Ministry of Culture and Tourism, the Revised Romanization of Korean. A third system--the Yale romanization system--exists, but is only used in academic literature. During the period of Russian interest in Korea at the beginning of the 20th century, attempts were also made at representing Korean in Cyrillic.
The McCune-Reischauer system is basically friendly to Westerners. For example, Korean has phonologically no distinction between voiced and voiceless consonants, but it phonetically distinguishes them. Aspirated consonants like "p'", "b'" and "t'" are distinguished by apostrophe from unaspirated ones, which is intuitive to Westerners. The apostrophe is also used to disambiguate syllables (jon'gum vs. jong'um).
However, since it is difficult to type them, the diacritic marks for vowels and consonants are often omitted, which caused serious confusion. In this case, "ŏ" (ㅓ) is simply written as "o" and "ŭ" (ㅡ) as "u". It becomes impossible to tell from "o" (ㅗ) and "u" (ㅜ). Lack of apostrophe makes it impossible to tell aspirated and unaspirated consonants.
The McCune-Reischauer system is purely based on anglophone spelling. In the beginning, most Westerners (non-english) will find it hard, to pronounce correctly.