Slovak ( slovenský jazyk (help·info), slovenčina, not to be confused with slovenski jezik or slovenščina, the native name of the Slovene language), is an Indo-European language that belongs to the West Slavic languages (together with Czech, Polish, Silesian, Kashubian, and Sorbian).

Slovak is the official language of Slovakia, where it is spoken by 5 million people. There are also Slovak speakers in the United States, the Czech Republic, Serbia, Ireland, Romania, Poland, Canada, Hungary, Croatia, The United Kingdom, Australia, Austria, and Ukraine.

Slovak uses a Latin script with small modifications that include the four diacritics (ˇ, ´, ¨, ˆ; see Pronunciation) placed above certain letters.

The primary principle of Slovak spelling is the phonemic principle, "Write as you hear". The secondary principle is the morphological principle: forms derived from the same stem are written in the same way even if they are pronounced differently. An example of this principle is the assimilation rule (see below). The tertiary principle is the etymological principle, which can be seen in the use of i after certain consonants and of y after other consonants, although both i and y are pronounced the same way. Finally there is the rarely applied grammatical principle, under which, for example, there is a difference in writing (but not in the pronunciation) between the basic singular and plural form of masculine adjectives, for example pekný (nice – sg.) vs pekní (nice – pl.), both pronounced [pekniː].