Westonbirt, The National Arboretum is an arboretum in Gloucestershire, England, about 3 miles (5 km) southwest of the town of Tetbury. Managed by Forestry England, it is perhaps the most important and widely known arboretum in the United Kingdom.
Planted in the heyday of Victorian plant hunting in the mid-19th century as part of the Westonbirt House estate, the arboretum forms part of a site which is listed Grade I on the Register of Historic Parks and Gardens of special historic interest.
There is evidence of coppicing at the site from 1292. First use of the name "Weston Birt" was in 1309. This was taken from Weston, a settlement to the west of Bowldown Road, and Birt from then lords of the manor, the Bret family.
The arboretum was established in 1829 by Robert Stayner Holford and was later extended by his son George Lindsay Holford. After the death of George in 1926, ownership of the arboretum passed to his nephew the fourth Earl of Morley, and eventually to the Forestry Commission in 1956 and Forestry England in 2019. The Holford family's mansion, Westonbirt House, became a girls' boarding school in 1927 when it was separated from the arboretum. Westonbirt Arboretum backs onto the Highgrove Estate of Prince Charles, the Prince of Wales.