Serbian language stems from the common Slavic spoken in the ancient homeland, on the North from the Carpathians. No written traces of that distant times exist, so that our knowledge of the structure of that common Slavic language is only the result of linguistic reconstruction that is based on the comparison of subsequent live Slavic languages. In linguistics, this hypothetical idiom is usually named by the term Proto-Slavic (or Common-Slavic). After the break of the Proto-Slavic people s community, its language broke too into three language groups: Eastern, Western and Southern. The clearly visible language specific treats within the Southern-Slavic group indicate that the Common Southern-Slavic language really existed. Due to the subsequent southward migrations of Southern-Slavic inhabitants, this idiom was separated in two parts: the Western Common South-Slavic and the Eastern Common South-Slavic languages. More recently, the Serbian descended from the Western part of Common South-Slavic. The creation of the Slavic orthography, in seventh decade of 9th Century A.D., had an extraordinary importance for the history of particular Slavic languages. Namely, since the break of the Common-Slavic language community up to the creation of the Slavic alphabet, only a relatively short period passed. Therefore the language structure that is very close to the structure of Common-Slavic in its late period of development is found in the oldest saved Slavic translations of religious books (10th - 11th Centuries A. D.). In these books, we find - actually - the first Slavic literary language, most frequently known under the name of Old-Church-Slavic (Old-Church-Slavonic) language. It functioned as the literary language in the whole Slavic world, which means that the Slavic language space owned two idioms that had their separate roles: one of the two (Old-Church-Slavic) served as the means of writing, transcription, preaching, church-singing, and the other one (secular) served as the means of everyday communication. The first one, in accordance with its function, generally did not change, while the second one went through a spontaneous development, which brought important changes of its forms. The description of development of Serbian secular language meets with certain difficulties due to the lack of its written form: the oldest saved documents in Serbian are dated by the end of the 12th Century. For the description of that pre-historic period of Serbian (the period from the break of proto-language until the end of 12th Century), the lateral sources - written texts in Old Church Slavonic, Greek and Latin, as well as the loan-words, names of places and modem dialects - have a great importance. The data collected from these sources are of great help to us, substantially in the description of the pre-historic period of the Serbian language development. The appearance of documents written in Serbian secular language at the end of 12th Century enabled the more complete and more exact study of the Serbian language history. After the appearance of those documents, we can follow the two parallel streams of Serbian literature: one with the use of literary (Church Slavonic) language, ant the other - with the use of Serbian secular language. The Miroslav s Gospel stands at the beginning of the first stream, and the signatures of Stephen Nemanja and duke Miroslav (1186), as well as the Charter of ban Kulin (1189) stand at the beginning of the second stream. The Cyrillic orthography characterizes both of them.