Danubian is a reconstruction of a prehistoric P-Celtic language, something like the common ancestor of the Gaulish and Brittonic languages. It is based as much on comparisons with other-than-Celtic ancient Indo-European languages (such as Sanskrit, Latin, Greek and Gothic) as on the attested Insular Celtic languages.

The approximate time setting for Danubian would be the first half of the first millenium BC (i.e. 1000 to 500 BC), and the geographical area would correspond with the core area of the Halstatt culture (i.e. northeastern France & southern Germany).