Eastern Orthodox missionaries, Saints Cyril and Methodius, developed the first script for a Slavic-speaking people, the Bulgarians, in the 800s. One of their disciples replaced their "Glagolithic" script with the "Cyrillic" we see today, using Greek letters whenever possible.
For some sounds that did not appear in Greek, two Hebrew letters were borrowed, "c" ("ts") and "sh."

After converting to Christianity in 865 AD, Bulgaria became an intellectual center for converting other Slavic peoples to Eastern Orthodoxy. By the end of the 900s, Eastern Orthodox Christianity and Cyrillic alphabets had spread to Macedonia, Serbia, and Rus (the forerunner of Russia, Belarus, and Ukraine).

The website
http://www.geocities.com/Athens/Academy/6490/language/alphabet.html
gives some early information about the Cyrillic alphabet.
More can be found by web searches against "Cyrillic" and "Glagolithic";
"Church Slavonic" (the liturgical language of the Russian Orthodox Church, a conduit for some terminology and grammatical forms from Bulgarian into Russian);
"Old Slavonic" (related to "Church Slavonic");
etc.

Return to alphabet pronunciation guide (without Cyrillic images).