The common brushtail possum is a nocturnal, semiarboreal marsupial of the family Phalangeridae, native to Australia and invasive in New Zealand, and the second-largest of the possums.

The Phalangeridae are a family of mostly nocturnal marsupials native to Australia, New Guinea, and Eastern Indonesia, including the cuscuses, brushtail possums, and their close relatives. Considered a type of possum, most species are arboreal, and they inhabit a wide range of forest habitats from alpine woodland to eucalypt forest and tropical jungle. Many species have been introduced to various non-native habitats by humans for thousands of years.