Zhuyin fuhao and Zhuyin are traditional terms, whereas Bopomofo is the colloquial term, also used by the ISO and Unicode. Consisting of 37 characters and four tone marks, it transcribes all possible sounds in Mandarin. Zhuyin was introduced in China by the Republican Government in the 1910s and used alongside the Wade-Giles system, which used a modified Latin alphabet. The Wade system was replaced by Hanyu Pinyin in 1958 by the Government of the People's Republic of China, and at the International Organization for Standardization (ISO) in 1982. Although Taiwan adopted Hanyu Pinyin as its official romanization system in 2009, Bopomofo is still an official transliteration system there and remains widely used as an educational tool and for electronic input methods.
The Commission on the Unification of Pronunciation, led by Wu Zhihui from 1912 to 1913, created a system called Zhuyin Zimu, which was based on Zhang Binglin's shorthand. A draft was released on July 11, 1913, by the Republic of China National Ministry of Education, but it was not officially proclaimed until November 23, 1928. It was later renamed first Guoyin Zimu and then, in April 1930, Zhuyin Fuhao. The last renaming addressed fears that the alphabetic system might independently replace Chinese characters.
In English translations, the system is often also called either Chu-yin or the Mandarin Phonetic Symbols. A romanized phonetic system was released in 1984 as Mandarin Phonetic Symbols II (MPS II).
Zhuyin was added to the Unicode Standard in October 1991 with the release of version 1.0.
Additional characters were added in September 1999 with the release of version 3.0.
The Unicode block for these additional characters, called Bopomofo Extended, is U+31A0–U+31BF: