The Heard Island and McDonald Islands are an Australian external territory and volcanic group of barren Antarctic islands, about two-thirds of the way from Madagascar to Antarctica, approximately 4,099 km southwest of Perth,3,845 km southwest of Cape Leeuwin, Australia, 4,200 km southeast of South Africa, 3,830 km southeast of Madagascar, 1,630 km north of Antarctica, and 450 km southeast of Kerguelen.
They are in the Southern Ocean according to the Australian definition but not according to the International Hydrographic Organization definition.
Discovered in the mid-19th century, they have been territories of Australia since 1947 and contain the only two active volcanoes in Australian territory, one of which, Mawson Peak, is the highest Australian mountain.
The group's overall size is 372 square kilometres (144 sq mi) in area and it has 101.9 km of coastline. The islands are uninhabited.