Slavic Languages

Scholars traditionally divide Slavic languages on the basis of geographical distribution into three main branches, some of which feature sub-branches:

East Slavic, extant: Russian, Ukrainian, Rusyn (a language or a dialect of Ukrainian), and Belarusian
West Slavic, which further subdivides into:
Czech and Slovak
Upper and Lower Sorbian (minority languages in Germany)
Lechitic languages: Polish, Pomeranian/Kashubian, Silesian and extinct Polabian
South Slavic, which further subdivides into:
Western subgroup composed of Slovene and Serbo-Croatian (Croatian, Bosnian, Serbian, Montenegrin).
Eastern subgroup composed of Bulgarian, and Macedonian
The oldest Slavic literary language was Old Church Slavonic, of which Church Slavonic is a later descendant
Some linguists speculate that a North Slavic branch has existed as well. The Old Novgorod dialect may have reflected some idiosyncrasies of this group. On the other hand, the term "North Slavic" is also used sometimes to combine the West and East Slavic languages into one group, in opposition to the South Slavic languages, due to traits the West and East Slavic branches share with each other that they do not with the South Slavic languages.

The most obvious differences between the West and East Slavic branches, are in orthography of standard languages; West Slavic languages are written in the Latin alphabet, and have had more Western European influence due to their speakers being historically Roman Catholic, whereas the East Slavic languages are written in the Cyrillic alphabet and with Eastern Orthodox or Uniate faithful, have had more Greek influence.

The tripartite division of the Slavic languages does not take into account the spoken dialects of each language. Of these, certain so-called transitional dialects and hybrid dialects often bridge the gaps between different languages, showing similarities that do not stand out when comparing Slavic literary (i.e., standard) languages. For example, Slovak (West Slavic) and Ukrainian (East Slavic) are bridged by eastern Slovak dialects, Rusyn[citation needed], and western Ukrainian dialects. Polish has similar transitionality with both western Ukrainian and Belarusian dialects.

Although the Slavic languages split from a common proto-language later than any other group of the Indo-European language family, enough differences exist between the various Slavic dialects and languages to make communication between speakers of different Slavic languages difficult. Within the individual Slavic languages, dialects may vary to a lesser degree, as those of Russian, or to a much greater degree, as those of Slovene.

http://en.wikipedia.org/wiki/Slavic_languages