The Treveri (Gaulish: *Treweroi) were a Germanic or Celtic tribe of the Belgae group who inhabited the lower valley of the Moselle in modern day Germany from around 150 BCE, if not earlier, until their displacement by the Franks. Their domain lay within the southern fringes of the Silva Arduenna (Ardennes Forest), a part of the vast Silva Carbonaria, in what are now Luxembourg, southeastern Belgium and western Germany; its centre was the city of Augusta Treverorum (Trier), to which the Treveri give their name. Celtic in language, according to Tacitus they claimed Germanic descent. They contained both Gallic and Germanic influences.

Although early adopters of Roman material culture, the Treveri had a chequered relationship with Roman power. Their leader Indutiomarus led them in revolt against Julius Caesar during the Gallic Wars; much later, they played a key role in the Gaulish revolt during the Year of the Four Emperors. On the other hand, the Treveri supplied the Roman army with some of its most famous cavalry, and the city of Augusta Treverorum was home for a time to the family of Germanicus, including the future emperor Gaius (Caligula). During the Crisis of the Third Century, the territory of the Treveri was overrun by Germanic Alamanni and Franks and later formed part of the Gallic Empire.

Under Constantine and his 4th-century successors, Augusta Treverorum became a large, favoured, rich and influential city that served as one of the capitals of the Roman Empire (together with Nicomedia (present-day İzmit, Turkey), Eboracum (present-day York, England),^{[citation needed]} Mediolanum (present-day Milan, Italy) and Sirmium). During this period, Christianity began to succeed the imperial cult and the worship of Roman and Celtic deities as the favoured religion of the city. Such Christian luminaries as Ambrose, Jerome, Martin of Tours and Athanasius of Alexandria spent time in Augusta Treverorum.

Among the surviving legacies of the ancient Treveri are Moselle wine from Luxembourg and Germany (introduced during Roman times) and the many Roman monuments of Trier and its surroundings, including neighbouring Luxembourg.

Three Roman roads, very important for their role in transregional trade and military deployment capability, went through the territory of the Treveri:

They are mentioned as Treveri by Caesar (mid-1st c. BC), Pliny (1st c. AD) and Tacitus (early 2nd c. AD), Trēoúēroi (Τρηούηροι) by Strabo (early 1st c. AD), Tríbēroi (Τρίβηροι) by Ptolemy (2nd c. AD), Trēouḗrōn (Τρηουήρων) by Cassius Dio (3rd c. AD), Treuerorum (gen.) by Orosius (early 5th c. AD), and as Triberorum in the Notitia Dignitatum (5th c. AD). The variant Treberi also appears in Pliny, and few highly deviant variant forms are also attested as Trēoũsgroi (Τρηου̃σγροι) in Strabo or Triḗrōn (Τριήρων) in Cassius Dio.

The first syllable is shown long and stressed (Trēverī) in Latin dictionaries, thus giving the Classical Latin pronunciation [ˈtreːwɛriː].

The ethnonym Trēverī is a latinized form of Gaulish *Trēueroi (sing. Trēueros). It is generally viewed as referring to 'crossing a river' or to a 'flowing river'. Linguists Rudolf Thurneysen and Xavier Delamarre have proposed to interpret the name as trē-uer- ('ferrymen'), composed of a suffix trē- (earlier *trei- 'through, across'; cf. Lat. trāns, Skt tiráh) attached to -uer- ('water, river'; cf. Skt vār, ON vari 'water'), This etymology is reinforced by the Old Irish cognate treóir (from *trē-uori-), meaning 'ford, place to cross a river'. The Treveri also had a special goddess called Ritona, which either means 'that of the ford' (from the stem ritu- 'ford') or 'that of the course' (from the homonym ritu-, rito- 'course'), and a temple dedicated to Uorioni Deo ('goddess of the watercourse').