Leadbeater's possum is a critically endangered possum largely restricted to small pockets of alpine ash, mountain ash, and snow gum forests in the Central Highlands of Victoria, Australia, north-east of Melbourne. It is primitive, relict, and non-gliding, and, as the only species in the petaurid genus Gymnobelideus, represents an ancestral form. Formerly, Leadbeater's possums were moderately common within the very small areas they inhabited; their requirement for year-round food supplies and tree-holes to take refuge in during the day restricts them to mixed-age wet sclerophyll forest with a dense mid-story of Acacia. The species was named in 1867 after John Leadbeater, the then taxidermist at the Museum Victoria. They also go by the common name of fairy possum. On 2 March 1971, the State of Victoria made the Leadbeater's possum its faunal emblem.

Phalangeriformes is a paraphyletic suborder of about 70 species of small to medium-sized arboreal marsupials native to Australia, New Guinea, and Sulawesi. The species are commonly known as possums, gliders, and cuscus. The common name "possum" for various Phalangeriformes species derives from the creatures' resemblance to the opossums of the Americas. However, although opossums are also marsupials, Australasian possums are more closely related to other Australasian marsupials such as kangaroos.