Kassite (also Cassite) was a language spoken by the Kassites in Mesopotamia from approximately the 18th to the 7th century BC. From the 16th to 12th centuries BC, kings of Kassite origin ruled in Babylon until they were overthrown by the Elamites. As only a few dozen words are known, none of which have been demonstrably linked to any living or dead language family, Kassite is considered an unclassified language at present, possibly an isolate or belonging to the Hurro-Urartian languages.

In the area known to have been inhabited by the Kassites the East Semitic Akkadian language was used, with the Sumerian language used for monumental and literary compositions. Traces of the Kassite language are few:

A lack of Kassite texts makes the reconstruction of Kassite grammar impossible at present.

Genetic relations of the Kassite language are unclear, although it is generally agreed that it was not Semitic; a relation with Elamite is doubtful.

Relationship with or membership in the Hurro-Urartian family has been suggested, based on a number of words.

The small corpus of Kassite words and vocabulary is collected and published by Balkan (1954) and Fournet (2011)