The Croatian language belongs to the South Slavic group of languages. It is the official language of the Republic of Croatia, and is also spoken by Croats in Bosnia and Herzegovina, Serbia (Vojvodina), Montenegro (Bay of Kotor), Austria (Burgenland), Italy (Molise), Hungary, Slovakia and Romania, and by Croatian émigrés in Western Europe, North and South America, Australia and New Zealand.

It has three dialects: Štokavian, Kajkavian and Čakavian, named after the interrogative pronouns što?, kaj? and ča? (the golden formula of the Croatian language). Today's standard literary language is mostly based on New Štokavian forms of Ijekavian pronunciation and is written using the Roman script. In the centuries following the migration of the Croats (6th and 7th centuries), Croatian developed primarily under the influence of Latin as the language of Western Christianity, while from the 10th century onwards, the influence of Old Church Slavonic played an important part, as it rapidly assimilated the features of its close relative, the native Croatian language (the Croatian version of Old Slavonic). In written documents, Croatian started to replace Old Slavonic in the 13th and 14th centuries and had replaced it completely by the end of the Middle Ages.

Glagolitic is the oldest Slavic script, thought to have been invented by St Cyril in the mid-9th century. It spread through Croatia as Angular Glagolitic, and from the 12th century onwards, the Croats were the only nation (apart from short Czech and Polish episodes in the 14th century, still facilitated by Croats) to use and develop Glagolitic, which remained in use until the end of the 19th century.

The Baška Tablet, an inscription of King Zvonimir's deed of donation and the construction of a church, is the most famous and one of the oldest monuments of the Croatian language, dated around 1100. This white limestone tablet, measuring 199 by 99.5 by 9 cm, bears the first record of the Croatian national name inscribed in the Croatian language.
The Šibenik Prayer, a prayer of praise to St Mary, one of the first Croatian linguistic and literary monuments written using Roman script, 1387.

As the Middle Ages turned into the modern age, the language was more and more influenced by Italian, German, Turkish and Hungarian, to some extent, while the influence of Czech was felt in the 19th and 20th centuries. Up to the 19th century, Croatian was mostly used in the form of written and literary dialects (Štokavian, Kajkavian and Čakavian). The Štokavian dialect entered Croatian literature at the end of the 15th century, and it was in fact at that time that the early history of modern literary Croatian began.

The Missal according to the Law of the Roman Court, the first printed Croatian book (22 February 1483), and the first liturgical book of the Roman rite that was not printed in the Latin language (Old Church Slavonic) or the Latin script (Glagolitic).
Dubrovnik Prayer Book, the first book printed in Croatian Cyrillic, 1512.

In the 16th century, Štokavian spread through a wider area of literary activity, and from the mid-18th century onwards, Štokavian as a literary language became firmly established, as did Kajkavian. Although there were projects in the 17th century to attempt to create a uniform Croatian language based on Štokavian, the duality of the Croatian standardising process was abandoned in the 19th century, at the time of the Illyrian Movement. New Štokavian was used as the skeleton around which, particularly in terms of the lexicon, Čakavian and Kajkavian elements were assembled, and with the introduction of diacritical marks (Ljudevit Gaj), a uniform way of writing the language was adopted. Thereafter, different schools of language developed (the Rijeka, Zadar, Zagreb and the so-called Vuk schools) which slowed down the natural development of the language, more or less separating it from Croatian written tradition.

Cyrillic is a Slavic script named after St Cyril, who is often considered its creator. It joined Glagolitic in Croatia in the 11th–12th century, and developed in an independent form, Croatian Cyrillic or Bosnian Cyrillic, and continued in use up to the mid-19th century.

During the time of the Yugoslav state (1918–1941 and 1945–1991), the development of standard Croatian was again hindered, and in 1954 the Novi Sad Agreement was reached, according to which Croats, Serbs and Montenegrins (at the time, Bosniacs were not acknowledged) agreed to introduce a compulsory common name for the language (Croato-Serbian, or Serbo-Croatian), produce a common orthography and lexicon, and standardise general scientific terminology.

Roman script uses the old Latin alphabet and refers to several graphic systems derived from it. Today, in various adaptations, Roman script is the main script of Europe, including Croatia (from the 14th century onwards). Croatian Roman script has 30 letters (sounds) of which three are digraphs (dž, lj, and nj) and five are written with diacritic marks (č, ć, đ, š and ž).

The Declaration on the Name and Position of the Croatian Literary Language (1967) sparked open opposition from the Croatian public to this language policy, so that in spite of the pressures to which Croatian was exposed, the process of making uniform standard forms of the two languages was never actually carried out. Although speakers of either language can understand each other, Croatian has developed in significantly different cultural and historical circumstances and today forms a quite separate South Slavic language, in the linguistic and particularly in the sociolinguistic sense.