Spelthorne is a local government district and borough in Surrey, England. It includes the towns of Ashford, Laleham, Shepperton, Staines-upon-Thames, Stanwell and Sunbury. Boroughs adjacent to Spelthorne include Runnymede and Elmbridge in Surrey, the Royal Borough of Windsor and Maidenhead, the London Borough of Hillingdon to the north, as well as the London Borough of Hounslow and the London Borough of Richmond upon Thames to the east. The borough is home to a number of large reservoirs, including Queen Mary, Staines and King George VI, all important bird reserves as is Staines Moor, designated an area of outstanding scientific interest.

Spelthorne appears in Domesday Book of 1086 as Spelet(h)orne, in Middlesex. Spelthorne was a hundred, an administrative area, where local leaders met about once a month. The Spelthorne hundred also covered East Bedfont, Feltham and Hanworth, all now in the London Borough of Hounslow in Greater London.

The borough was formed in 1974 from Staines Urban District and Sunbury-on-Thames Urban District. The urban districts had originally been part of Middlesex; however in 1965 when much of the rest of Middlesex was absorbed into Greater London these two were instead transferred to Surrey. Its boundary changed in 1995 when Poyle was transferred to Slough in Berkshire. The borough remained inside the Metropolitan Police District, and was not transferred to Surrey Police until the boundary was realigned to Greater London in 2000.