Russian , Serbian (see Serbo-Croatian language ), {{link=Bulgarian language">Bulgarian and Macedonian, Belarusian , Ukrainian , and many non-Slavic languages of the former Soviet Union, as well as Khalka Mongolian (see Mongolian language ).
The history of the Cyrillic alphabet is complex and much disputed. It is clearly derived from 9th-century Greek uncial capital letters, with the non-Greek letters probably taken from the Glagolitic alphabet, a highly original alphabet in which (along with Cyrillic) Old Church Slavonic was written. A commonly held hypothesis is that followers of Sts. Cyril and Methodius developed Cyrillic in the southern Balkans around the end of the 9th century. The 44 original Cyrillic letters were reduced in number in most later alphabets used for vernacular languages, and some wholly original letters introduced, particularly for non-Slavic languages.