Capreolus is a genus of deer, the roe deer. It contains two species native to Eurasia, and fossil evidence also supports their former presence in North America.

English roe is from Old English ra or rá, from raha, from Proto-Germanic *raikhaz, cognate to Old Norse ra, Old Saxon reho, Middle Dutch and Dutch ree, Old High German reh, German Reh. It is perhaps ultimately derived from a PIE root *rei-, meaning "streaked, spotted or striped".

The word is attested on the 5th-century Caistor-by-Norwich astragalus -a roe deer talus bone, written in Elder Futhark as ᚱᚨᛇᚺᚨᚾ, transliterated as raïhan.

In the English language this animal was originally simply called a 'roe', but over time the word 'roe' has become a qualifier and the creature is now usually called a 'roe deer'.

The Koiné Greek name πύγαργος, transliterated 'pygargos', mentioned in the Septuagint and the works of various writers such as Hesychius, Herodotus and later Pliny, was originally thought to refer to this species (in many European translations of the Bible), although it is now more often believed to refer to the addax. It is derived from the words pyge 'buttocks' and argo 'white'.

The taxonomic name Capreolus is derived from capra or caprea, meaning 'billy goat', with the diminutive suffix -olus. The meaning of this word in Latin is not entirely clear: it may have meant 'ibex' or 'chamois'. The roe deer was also known as capraginus or capruginus in Latin.

Roe deer are most closely related to the water deer Hydropotes, and, counterintuitively, the three species in this group, called the Capreolini, are most closely related to elk and moose Alces.

Although roe deer were once classified as belonging to the subfamily Cervinae, they are now classified as part of the Capreolinae, which includes the deer from the New World.