Foulness Island () is a closed island on the east coast of Essex in England, which is separated from the mainland by narrow creeks. In the 2001 census, the usually resident population of the civil parish was 212, living in the settlements of Churchend and Courtsend, at the north end of the island. The population reduced to 151 at the 2011 Census. The island had until recently a general store and post office. The George and Dragon pub in Churchend closed in 2007, while the church of St Mary the Virgin closed in May 2010. In 2019, the Southend Echo reported plans for the church to be converted into a five-bedroom home.

Foulness Island is predominantly farmland and is protected from the sea by a sea wall. The island's unusual name is derived from the Old English fugla næsse ("bird headland"), referring to wildfowl. It is an internationally important site for migrating and breeding birds, including pied avocets. During the North Sea flood of 1953, almost the entire island was flooded and two people died.

Before 1922, when the military road was built, the only access was across the Maplin Sands via the Broomway, a tidal path said to predate the Romans, or by boat. Public rights of way exist, but the island is now run by QinetiQ on behalf of the Ministry of Defence as MoD Shoeburyness with access to the island by non-residents subject to stringent times and restrictions.