In Celtic mythology, Bel, Belenos (also Belenus) was a deity worshipped in Gaul, Cisalpine Gaul, and Celtic areas of Austria, Britain and Spain. He is particularly associated with Cornwall, West Cornwall being anciently called Belerion, the place of Bel. He was the Celtic sun god and had shrines from Aquileia on the Adriatic to Kirkby Lonsdale in England.

The etymology of the name is unclear. Suggestions include "shining one," "the bright one" and "henbane god".

In the Roman period he was identified with Apollo. There are currently 51 known inscriptions dedicated to Belenus, mainly concentrated in Aquileia and Cisalpine Gaul, but also extend into Gallia Narbonensis, Noricum, and far beyond. Images of Belenus sometimes show him to be accompanied by a female, thought to be the Gaulish deity Belisama.

In ancient Gaul and Britain, Apollo may have been equated with fifteen or more different Celtic names and epithets (notably Grannos, Borvo, Maponus, Moritasgus and others). The legendary king Belenus in Geoffrey of Monmouth's History of the Kings of Britain is probably also derived from this god. The name of the ancient British king Cunobelinus means "hound of Belinos".