Lithuanian (lietuvių kalba) is a Baltic language spoken in the Baltic region. It is the language of Lithuanians and the official language of Lithuania as well as one of the official languages of the European Union. There are about 2.9 million native Lithuanian speakers in Lithuania and about 200,000 abroad.
As a Baltic language, Lithuanian is closely related to neighbouring Latvian and more distantly to Slavic, Germanic and other Indo-European languages. It is written in a Latin alphabet. Lithuanian is often said to be the most conservative living Indo-European language, retaining features of Proto-Indo-European now lost in other languages.
Among Indo-European languages, Lithuanian is conservative in some aspects of its grammar and phonology, retaining archaic features otherwise found only in ancient languages such as Sanskrit (particularly its early form, Vedic Sanskrit) or Ancient Greek. For this reason, it is an important source for the reconstruction of the Proto-Indo-European language despite its late attestation (with the earliest texts dating only to c. undefined 1500).
Lithuanian was studied by linguists such as Franz Bopp, August Schleicher, Adalbert Bezzenberger, Louis Hjelmslev, Ferdinand de Saussure, Winfred P. Lehmann and Vladimir Toporov and others.
The Proto-Balto-Slavic languages branched off directly from Proto-Indo-European, then sub-branched into Proto-Baltic and Proto-Slavic. Proto-Baltic branched off into Proto-West Baltic and Proto-East Baltic. Baltic languages passed through a Proto-Balto-Slavic stage, from which Baltic languages retain numerous exclusive and non-exclusive lexical, morphological, phonological and accentual isoglosses in common with the Slavic languages, which represent their closest living Indo-European relatives. Moreover, with Lithuanian being so archaic in phonology, Slavic words can often be deduced from Lithuanian by regular sound laws; for example, Lith. vilkas and Polish wilk ← PBSl. *wilkas (cf. PSl. *vьlkъ) ← PIE *wĺ̥kʷos, all meaning "wolf".
According to some glottochronological speculations, the Eastern Baltic languages split from the Western Baltic ones between AD 400 and 600. The Greek geographer Ptolemy had already written of two Baltic tribe/nations by name, the Galindai and Sudinoi (Γαλίνδαι, Σουδινοί) in the 2nd century AD. The differentiation between Lithuanian and Latvian started after 800; for a long period, they could be considered dialects of a single language. At a minimum, transitional dialects existed until the 14th or 15th century and perhaps as late as the 17th century. Also, the 13th- and 14th-century occupation of the western part of the Daugava basin (closely coinciding with the territory of modern Latvia) by the German Sword Brethren had a significant influence on the languages' independent development.
The earliest surviving written Lithuanian text is a translation dating from about 1503–1525 of the Lord's Prayer, the Hail Mary, and the Nicene Creed written in the Southern Aukštaitian dialect. Printed books existed after 1547, but the level of literacy among Lithuanians was low through the 18th century, and books were not commonly available. In 1864, following the January Uprising, Mikhail Muravyov, the Russian Governor General of Lithuania, banned the language in education and publishing and barred use of the Latin alphabet altogether, although books printed in Lithuanian continued to be printed across the border in East Prussia and in the United States. Brought into the country by book smugglers despite the threat of stiff prison sentences, they helped fuel a growing nationalist sentiment that finally led to the lifting of the ban in 1904.
Jonas Jablonskis (1860–1930) made significant contributions to the formation of the standard Lithuanian language. The conventions of written Lithuanian had been evolving during the 19th century, but Jablonskis, in the introduction to his Lietuviškos kalbos gramatika, was the first to formulate and expound the essential principles that were so indispensable to its later development. His proposal for Standard Lithuanian was based on his native Western Aukštaitijan dialect with some features of the eastern Prussian Lithuanians' dialect spoken in Lithuania Minor. These dialects had preserved archaic phonetics mostly intact due to the influence of the neighbouring Old Prussian language, while the other dialects had experienced different phonetic shifts. Lithuanian has been the official language of Lithuania since 1918. During the Soviet era (see History of Lithuania), it was used in official discourse along with Russian, which, as the official language of the USSR, took precedence over Lithuanian.