Idmiston is a village and civil parish in Wiltshire, England. The village is about 3 miles (4.8 km) southeast of Amesbury and 6 miles (10 km) northeast of Salisbury. The parish includes the villages of Porton and Gomeldon; all three villages are on the River Bourne and are linked by the A338 road. Porton Down military science park is in the parish, separated from Idmiston by a railway line. It is home to the Defence Science and Technology Laboratory and related businesses.