Sugar gliders are gliding possums native to Australia, Indonesia, and New Guinea. They are in the genus Petaurus, and the species breviceps. The literal translation of this is short-headed rope dancer. Gliders are in the mammalia class, and the marsupial infraclass. Marsupials' pouches distinguish them from the other two kinds of mammals: eutherians, which are mammals with placental births like humans, and monotremes, which are the egg-laying mammals - platypus and echidna.
There are 10 families within the diprotodontia order. Among them there are six possum families: Pseudocheiridae, Petauridae, Acrobatidae, Tarsipedidae, Phalangeridae and Burramyidae. Kangaroos (Macropodidae), kangaroo-rats, (Potoroidae), koalas (Phascolarctidae), and wombats (Vombatidae) also share this order.
If you live in North America, it's likely that when you hear the word possum you think of an opossum, however opossums are in the Monodelphis genus and originate from South America. Sugar gliders and opossums are both marsupials, but are in different orders: diprotodontia and didelphimorphia, respectively. According to this study, opossums and sugar gliders are in the least related marsupial orders.
The Petaurus genus is full of flying phalangers like sugar gliders, including squirrel gliders, mahogany gliders, Northern gliders, yellow-bellied gliders, and biak gliders, pictured in order below. Click here for more info on the Petaurus genus.
A sugar glider looks quite a bit like a flying squirrel, but the two are not closely related, making this an excellent example of convergent evolution. Flying squirrels are in the order rodentia, while sugar gliders are diprotodontia. However, both species are nocturnal, arboreal mammals that have independently evolved gliding membranes, called patagiums, for getting around in high tree branches.
Their biological similarities end there though. Sugar gliders are marsupials, while squirrels are eutherians (like us), which hints at the dramatic differences in internal biology between these two doppelgangers.