- Language: Old Frankish
- Alternate names:
- Language code: frk
- Language family: Indo-European, Classical Indo-European, Germanic, Northwest Germanic, West Germanic, Macro-Dutch, Old Dutch-Old Frankish
- Number of speakers: Extinct
- Script: Latin script
Old Frankish was the language of the Franks and it is classified as a West Germanic language. Once it was spoken in areas covering modern Belgium, the Netherlands, Luxembourg and adjacent parts of France and Germany.
The Franks are descended from Germanic tribes from the Nordic countries that settled parts of the Netherlands and western Germany during the early Iron Age. From the 4th century they are attested as moving from the Roman Empire into what is now the southern Netherlands and northern Belgium. In the 5th and 6th century they expanded their realm and dominated Roman Gaul completely as well as client states such as Bavaria and Thuringen.
By the year 900 Frankish had evolved into Old Low Franconian in the area that was originally held by Franks of the 4th century (e.g.Flanders), while in Valois (Picardy) and Île-de-France (Paris) it was replaced by Old French as the dominating language.