Wade-Giles was the main system of transliteration in the English-speaking world for much of the 20th century. It is used in several standard reference books. It is also used in all books about China published before 1979. It replaced the Nanjing-based romanization systems that was common until the late 19th century. Wade-Giles has been replaced by the Pinyin system today. It still remains in use in Taiwan (Republic of China).