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.
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 Belinus 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".
An epithet of Belenus may have been Vindonnus. Apollo Vindonnus had a temple at Essarois near Châtillon-sur-Seine in Burgundy. The sanctuary was based on a curative spring. Part of the temple pediment survives, bearing an inscription to the god and to the spirit of the springs and, above it, the head of a radiate sun-deity. Many votive objects were brought to the shrine, some of oak, and some of stone. Some offerings take the form of images of hands holding fruit or a cake; others represent the parts of the body requiring a cure. In many cases the pilgrims appear to have suffered from eye afflictions.
Teutorix has been suggested as an epithet of Belenus as borrowed into Germanic religion.
Name variants 
- Belanu, amongst the Ligurians
- Belyn in Welsh
- Llywelyn, Belenus forms the root for the welyn in this compound Welsh name (w < b).
- Nicole Jufer & Thierry Luginbühl (2001). Les dieux gaulois : répertoire des noms de divinités celtiques connus par l'épigraphie, les textes antiques et la toponymie. Paris: Editions Errance. ISBN 2-87772-200-7.
- www.Roman-Britain.org. Roman Inscriptions of Britain (RIB 611).
- Mythology - General Editor C. Scott ISBN 978-1-84483-061-9
- Koch, John T. (2006). Celtic Culture: A Historical Encyclopedia. Santa Barbara: ABC-CLIO, Inc. ISBN 1-85109-440-7.
- Peter Schrijver, "On Henbane and Early European Narcotics", Zeitschrift für celtische Philologie vol.51 (1999), pp.17-45
- Dictionary of Celtic Myth and Legend. Miranda Green. Thames and Hudson Ltd. London. 1997