The primary difference between marsupials and the other mammals is that the young are carried by the female in a pouch until they are developed well enough to fend for themselves. The 300 species of marsupials include kangaroos, the koala, wombats, bandicoots, bilbies, and some moles. Most of these live in or near Australia. About 94 species of opossums live in the Americas, with the Virginia opossum being the only one in North America.

The majority of the Australian-region marsupials (157) belong to a group characterized by two enlarged lower front teeth. This group includes all of the kangaroo relatives, cuscuses (a type of possum), koalas, and wombats. Cuscuses, or possums, have two toes on their hind feet fused together. Kangaroos and their relatives have the long feet and their unique hopping gait when they run. The koala is the only mammal that has two opposable digits on its feet, so both digits function like thumbs. Koalas are arboreal, while their close cousins the wombats are terrestrial.