Beverston Castle, also known as Beverstone Castle or Tetbury Castle, is a castle in the village of Beverston, Gloucestershire, England. It was constructed as a medieval stone fortress. The property is a mix of manor house, various small buildings, extensive gardens, and the medieval ruins of the fortified building. The castle was founded in 1229 by Maurice de Gaunt.

Much of the castle was in a state of ruin according to a 2019 report, and had been uninhabitable since the 17th century. Several buildings on the 693-acre property, including five cottages and the 17th-century house with seven bedrooms, were in use as residences, however.

The original castle was laid out in pentagonal plan. In the early 14th century, a small quadrangular stronghold was added, along with a twin-towered gatehouse. Beverston Castle is situated approximately three kilometres west of the town of Tetbury and about two kilometres east of the medieval abbey annex, Calcot Manor. The castle is in the Cotswolds, a designated National Landscape.

Early Roman remains have been found nearby, at Calcot Manor, indicating habitation of this area as early as the 5th century, although it is likely that earlier Iron Age peoples would have also been in this locale. In the Middle Ages it was called Beverstane, and in medieval times the site was known as Beverstone. Another early name for this site was Bureston, derived from the large number of blue stones found here.

The site was the location of an important battle circa 1140 AD between the opposing English armies of King Stephen and Empress Matilda during The Anarchy.

The feudal barony of Beverston was founded by Robert Fitzharding (c. 1095–1170), an Anglo-Saxon nobleman who was also granted the feudal barony of Berkeley in Gloucestershire. He rebuilt Berkeley Castle, and founded the Berkeley family which still occupies it today. He granted his subsidiary barony of Beverston, with its castle, to his third son Robert FitzRobert Fitzharding (d.1194), who adopted the surname "de Gaunt" and who by his second wife Avice had a son and heir Maurice de Gaunt (1184-1230) who died without issue. Whilst Robert Fitzharding, the patriarch of the Berkeley family, founded St Augustine's Abbey in Bristol (now Bristol Cathedral), the de Gaunts founded "The Gaunts' Chapel" (now called "St Mark's Church" or "The Mayor's Chapel") opposite it, across what is today College Green. The crossed-legged effigies supposed to represent Maurice de Gaunt and his father, survive in the Gaunts' Chapel, together with two monuments to later members of the Berkeley family of Stoke Gifford, Gloucestershire (a junior branch descended from Maurice de Berkeley, 2nd Baron Berkeley, 7th feudal baron of Berkeley (1271–1326), Maurice the Magnanimous of Berkeley Castle).

In 1225 Maurice de Gaunt built a fortified manor house at Beverston without a royal licence, and was subsequently granted by the king a licence to crenellate. On 29 July 1229, King Henry III signed a document allowing the castle to stand and remain for ever. Maurice de Gaunt was also known as Maurice de Ghent or de Gant, and as Maurice Paynel; Beverston was called Beverestan in the July 1229 document which was written in Latin. On the death of Maurice de Gaunt in 1230 without issue, his heir to the feudal barony of Beverston was Robert de Gournay (d.1269), the son of his half-sister Eve de Gaunt by her husband Anselm de Gournay. In 1235 the manors of Beverston, Elberton and King's Weston were held by Robert de Gournay, as a tenant-in-chief of the king, for the service of one knight's fee. The last in the male line was John de Gournay (d.1291) who left a daughter and heiress Elizabeth de Gournay. At about this time Beverston passed back to the senior line of the Berkeley family and was granted (with extensive other estates) by Thomas de Berkeley, 3rd Baron Berkeley, 8th feudal baron of Berkeley (1293/6–1361) Thomas the Rich to his 4th son Sir John Berkeley (1352-1428), founder of the Beverston line of that family.

This early castle was fortified by a T-shaped ditch, part of which is still intact in the survival of a partial moat on the south side of the castle. In 1330 the castle was extensively remodeled by Thomas de Berkeley, 3rd Baron Berkeley (Thomas the Rich), who erected a small quadrangular stronghold, with a twin-towered gatehouse. A smaller square tower was added in the late 15th century. At an unspecified later date, an adjoining house was added, using parts of the original structure.