Selonian was a language appertaining to the Baltic languages group of the Indo-European languages family. This language was spoken by the Selonians who lived until the 15th century in Eastern Latvia and North-Eastern Lithuania. They were a small Baltic tribe (now extinct) and their neighbours were predominantly Slavs and the Selonian was probably had been influenced by Russians as we see in the place names.

After the Grand Duchy of Lithuania was established, it comprised all the minor tribes, including the Selonians, who were assimilated and in the next century lost their language that became extinct.

The traces of the Selonian language can be still found in the territories Selonians inhabited, especially in the accent and phonetics.