Gaulish is an extinct Celtic language spoken in parts of Continental Europe before and during the period of the Roman Empire. In the narrow sense, Gaulish was the language of the Celts of Gaul (now France, Luxembourg, Belgium, most of Switzerland, Northern Italy, as well as the parts of the Netherlands and Germany on the west bank of the Rhine). In a wider sense, it also comprises varieties of Celtic that were spoken across much of central Europe ("Noric"), parts of the Balkans, and Anatolia ("Galatian"), which are thought to have been closely related. The more divergent Lepontic of Northern Italy has also sometimes been subsumed under Gaulish.
Together with Lepontic and the Celtiberian spoken in the Iberian Peninsula, Gaulish helps form the geographic group of Continental Celtic languages. The precise linguistic relationships among them, as well as between them and the modern Insular Celtic languages, are uncertain and a matter of ongoing debate because of their sparse attestation.
Gaulish is found in some 800 (often fragmentary) inscriptions including calendars, pottery accounts, funeral monuments, short dedications to gods, coin inscriptions, statements of ownership, and other texts, possibly curse tablets. Gaulish was first written in Greek script in southern France and in a variety of Old Italic script in northern Italy. After the Roman conquest of those regions, writing shifted to Latin script. During his conquest of Gaul, Caesar reported that the Helvetii were in possession of documents in the Greek script, and all Gaulish coins used the Greek script until about 50 BC.
Gaulish in Western Europe was supplanted by Vulgar Latin and various Germanic languages from around the 5th century AD onward. It is thought to have been a living language well into the 6th century.
The legacy of Gaulish can be observed in the modern French language, in which a couple of hundred words are derived from the extinct Celtic language; and through extensive French influence, in the English language as well.