The Helvetii were a Gallic 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 only names 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 (58 BC) serving as a catalyst for Caesar's conquest of Gaul.
The endonym Helvetii is mostly derived from a Gaulish elu-, meaning "gain, prosperity" or "multitude", cognate with Welsh elw and Old Irish prefix il-, meaning "many" or "multiple" (from the PIE root *pelh1u- "many"). The second part of the name has sometimes been interpreted as *etu-, "terrain, grassland", thus interpreting the tribal name as "rich in land".
The earliest attestation of the name is found in a graffito on a vessel from Mantua, dated to c. 300 BC. The inscription in Etruscan letters reads eluveitie, which has been interpreted as the Etruscan form of the Celtic elu̯eti̯os ("the Helvetian"), presumably referring to a man of Helvetian descent living in Mantua.
The name of the national personification of Switzerland, Helvetia, and the country's Neo-Latin name, Confoederatio Helvetica, are both derived from the name of the Helvetii.