Serbian-Slavonic                                                         ŃSL
Miroslav Gospel (detail), the oldest preserved Serbian manuscript (1196)

In  the medieval Serbia two, not so distinct, languages were in use. Serbian, spoken by ordinary people which was to some extent used also for official documents (letters, charts, legislative acts etc.) and Serbian-Slavonic, used in literature. The latter is a version of the Old Slavonic, with some differences in phonology and to a lesser degree in morphology, due to influence of Serbian. 
Serbian medieval literature written in Serbian-Slavonic is characterized by variety of genres (the lives of  saints, prayers, eulogies etc.). By preserving the firm structure of the Old-Slavonic language, Serbian-Slavonic had great expressive potentials (e.g. compounds and participal constructions). As noted, the influence of Serbian altered to some extent its phonetic properties, thus providing better communication between text and reader (listener). As a consequence, text written in Serbian-Slavonic sounded familiar and was easy to understand. The other influence of Serbian is manifested in vocabulary: words used in popular language became part of standard Serbian-Slavonic vocabulary, which made this language distinct from other versions of Old-Slavonic (i.e. Russian-Slavonic and Bulgarian-Slavonic). The fact that some manuscripts were translated from, say, Russian-Slavonic to Serbian-Slavonic indicates that those were indeed distinct languages. However, similarities among those languages were greater than their differences.  Thus, for example, it was not so rare that the same manuscript was alternatively written in all three langauges.
Orthography: The written form of Serbian-Slavonic could be traced from 12th century on. Miroslav Gospel (around 1185), the oldest preserved manuscript, could be taken as an indirect testimony of the oldest Serbian orthorgaphy (zetsko-humska), followed by the Rasian (Ra?ka) orthography in the 13th and the 14th century, created under the inflence of St. Sava. Texts from the end of the 14th and the begining of the 15th century are mainly written in orthography developed at monastery Resava orthographic circle. This orthographic reform was theoretically elaborated by Constantine the Philosopher, the biographer of despotes Stefan Lazarevi?. The written form of Serbian-Slavonic lasts till the begining of the 18th century as a mixture of Rasian and Resavian orthography. In the middle of the 18th century Serbian-Slavonic was gradually substituted by Russian-Slavonic or NeoRussian-Slavonic. 
There are three aspects that define the character of old Serbian literature. Those are Orthodox Christianity, spiritual influence of Byzantine civilization and Serbian-Slavonic language. Serbian-Slavonic nad?ivljava independent medieval Serbian state, and spreads beyond its state and church boundaries. It unites Serbian, Zetian and Bosnian regions, but also Holly Mountain and, to some extent, Constantinopolis, Sinay and Jerusalem.