Rheged was a nation in Dark Ages Britain. It was situated in what is now north-western England and south-western Scotland. It was founded after the Roman Empire abandoned Britain, which may put the date in the fifth century. Rheged royal genealogies trace later kings back to Coel Hen (Old King Cole), who appears to have ruled in the early 5th century. The victories of its kings Urien Rheged, and his son Owen mab Urien, over the chieftains of Bernicia in the second half of the sixth century, were celebrated by the bard Taliesin. Following Bernicia's union with Deira to become the kingdom of Northumbria, Rheged itself was annexed into Northumbria, at some time before AD 730. There is some evidence that Rheged was incorporated into Northumbria by royal marriage in 633.

The language of the Rheged ruling classes, and quite likely of the majority of the population, was a Brythonic language somewhat similar to Welsh.

Place-name evidence and Taliesin's poems suggest that Rheged included all of what is now Dumfries and Galloway and Cumbria, plus Lancashire at least as far south as Oldham, and the Dales including Wensleydale and Catterick. It may well also have included Northumberland and Durham prior to the conquest of these lands by Bernicia and later Northumbria. The royal family apparently had two principal caers (castles / capital cities), one at Caer Llewelyd (identified with Carlisle), and one at Catraeth (Catterick).

The language of Northumbria was Old English.

There is considerable evidence for an Irish presence as well. It is known that Irish Christian missionaries were active in Rheged (although the region was at least nominally Christian even in Roman times) and there were likely Irish traders, pirates and settlers unconnected with the church as well.

One of the more accessible sources for Rheged history (and dark ages British history generally) is the works of the Venerable Bede.

The name Rheged has been adopted by the Rheged Centre close to Penrith, Cumbria. The centre, apart from having a number of retail outlets, boasts the largest turf roof in Europe and a giant cinema screen which shows films including one about the history of Rheged.