The Koala is a thickset arboreal marsupial herbivore native to Australia, and the only extant representative of the family Phascolarctidae.

The Koala is found all along the eastern coast of Australia from near Adelaide to the southern part of Cape York Peninsula, and as far into the hinterland as there is enough rainfall to support suitable forests. The Koalas of South Australia were largely exterminated during the early part of the 20th century, but the state has since been repopulated with Victorian stock. The Koala is not found in Tasmania or Western Australia.

The word "koala" comes from the Dharuk word gula. Closely related words appear in other Australian Aboriginal languages, including:

• The Ngunnawal of the Canberra region also call it gula.
• In the Blue Mountains of New South Wales, Aborigines called Koalas by the word Cullawines.
• In the Murray Region, Aborigines called Koalas by the word Karbors.
• Other Aboriginal names for Koalas include: Bangaroos, Koolewongs, Narnagoons and Cholos.

It is commonly said that the common name 'Koala' is an Aboriginal word meaning "no drink" although there is no evidence to support this. Koalas do drink water, but only rarely, due to their diet consisting of eucalypt leaves, which contain sufficient water to obviate the need for the Koala to descend to ground level to drink.

Early European settlers to Australia called the Koala the Native Bear, and the Koala is still sometimes called the Koala Bear, but it is not a member of the bear family. It is not even a placental mammal (which most mammals are) - it is a marsupial. The Koala's scientific name (Phascolarctos cinereus) comes from the Greek: phaskolos meaning "pouch" and; arktos meaning "bear". The cinereus epithet is Latin and means "ash-coloured".