The Helvetii, anglicized as Helvetians, were a Celtic tribe or tribal confederation occupying most of the Swiss plateau at the time of their contact with the Roman Republic in the 1st century BC. According to Julius Caesar, the Helvetians were divided into four subgroups or pagi. Of these, Caesar names only the Verbigeni and the Tigurini, while Posidonius mentions the Tigurini and the Tougeni (Τωυγενοί). They feature prominently in the Commentaries on the Gallic War, with their failed migration attempt to southwestern Gaul serving as a catalyst for Caesar's conquest of Gaul.

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. 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.