Latvian belongs to the Eastern Baltic sub-group of the Baltic language group in the Indo-European language family . Of the Baltic languages, only Latvian and its closest relative Lithuanian remain. However, while related, the Latvian and Lithuanian vocabularies vary greatly from each other and are not mutually intelligible.

The Baltic languages are of particular interest to linguists because they retain many archaic features believed to have been present in the early stages of the Proto-Indo-European language .

There is evidence to suggest the existence of a Balto-Slavic language group after the break-up of Proto-Indo-European, with the Slavic and Baltic languages then splitting perhaps around the 10th century BC. However, this is disputed by many linguists. While the possession of many archaic features is undeniable, the exact manner by which the Baltic languages have developed from the Proto-Indo-European language is not clear.

The Eastern Baltic languages split from the Western Baltic ones (or, perhaps, from the hypothetic proto-Baltic language) between 400 and 600 . The differentiation between Lithuanian and Latvian started after 800 , with a long period of being one language but different dialects. At a minimum, transitional dialects existed until the 14th century or 15th century, and perhaps as late as the 17th century.

Latvian emerged as a distinct language in the 16th century , having evolved from Latgalian and assimilating Curonian , Semigallian and Selonian on the way. All of these belong to the Baltic language group .

The oldest known examples of written Latvian are from a 1530 translation of a hymn made by Nicholas Ramm, a German pastor in Riga .