Porton Down is a science and defence technology campus in Wiltshire, England, just north-east of the village of Porton, near Salisbury. It is home to two British government facilities: a site of the Ministry of Defence's Defence Science and Technology Laboratory – known for over 100 years as one of the UK's most secretive and controversial military research facilities, occupying 7,000 acres (2,800 ha) – and a site of the UK Health Security Agency. Since 2018, part of the campus has housed Porton Science Park, which is owned and operated by Wiltshire Council and has private sector companies in the health, life science and defence and security sectors.

Porton is a village in the Bourne valley, Wiltshire, England, about 5 miles (8 km) northeast of Salisbury. It is the largest settlement in Idmiston civil parish.