Old Prussian was a West Baltic language belonging to the Baltic branch of the Indo-European languages, which was once spoken by the Old Prussians, the Baltic peoples of the Prussian region. The language is called Old Prussian to avoid confusion with the German dialects of Low Prussian and High Prussian and with the adjective Prussian as it relates to the later German state. Old Prussian began to be written down in the Latin alphabet in about the 13th century, and a small amount of literature in the language survives.

The Baltic languages are a branch of the Indo-European language family spoken natively or as a second language by a population of about 6.5–7.0 million people mainly in areas extending east and southeast of the Baltic Sea in Europe. Together with the Slavic languages, they form the Balto-Slavic branch of the Indo-European family.