West Slavic language closely related to Czech (Czech language), Polish (Polish language), and the Sorbian (Sorbian languages) languages of eastern Germany. It is the official language of Slovakia. Slovak is written in the Roman (Latin) alphabet. Although there are traces of the Slovak language in Latin documents of the 11th–15th century and in the Czech of the 14th–16th century, the earliest-known attempts to increase the use of written Slovak came in the 17th and 18th centuries, when Roman Catholics centred at the University of Trnava tried to introduce Slovak for use in their hymnal and other church books. The language did not become accepted as a literary language, however, until a group led by the Protestant L'udovít Štúr (1815–56) began to write in the central Slovak dialects. The language of these writings, as modified and codified by Martin Hattala in his grammar of 1852, rapidly gained approval and was accepted as standard.

There are three major Slovak dialect groups: Eastern, Central, and Western. The Western dialects of Slovak shade into the Moravian dialects of the Czech language. Except for perhaps the extreme Eastern Slovak dialects and the Bohemian Czech dialect, all dialects of Slovak and Czech are mutually comprehensible, for there are no sharp linguistic frontiers. In general, Slovak has been more conservative phonetically, while Czech has undergone far-reaching changes since the 14th century; thus, Slovak has retained long syllabic l and r and a series of diphthongs. Slovak did not develop the distinctive sibilant ř sound of Czech.