The Baltic languages are a branch of the Indo-European language family spoken natively by a population of about 4.5 million people mainly in areas extending east and southeast of the Baltic Sea in Northern Europe. Together with the Slavic languages, they form the Balto-Slavic branch of the Indo-European family.

Scholars usually regard them as a single subgroup divided into two branches: Western Baltic (containing only extinct languages) and Eastern Baltic (containing at least two living languages, Lithuanian, Latvian, and by some counts including Latgalian and Samogitian as separate languages rather than dialects of the two aforementioned languages). The range of the Eastern Baltic linguistic influence once possibly reached as far as the Ural Mountains, but this hypothesis has been questioned.

Old Prussian, a Western Baltic language that became extinct in the 18th century, has possibly retained the greatest number of properties from Proto-Baltic.

Although related, the Lithuanian, Latvian and, particularly, Old Prussian lexicons differ substantially from one another, and as such they are/were not mutually intelligible. Relatively low mutual interaction for neighbouring languages historically led to gradual erosion of mutual intelligibility; development of their respective linguistic innovations that did not exist in shared Proto-Baltic and as well as substantial number of false friends and various uses and sources of loanwords from their surrounding languages are considered the major reasons for poor mutual intelligibility today.