Two groups of rodents are referred to as flying squirrels. They are:
- the subfamily Petauristinae of the Sciuridae, the group that includes the typical squirrels. Flying squirrels of this group are mainly found in Asia, but extend to Europe (Finland) and North America.
- the scaly-tailed flying squirrels of the family Anomaluridae, found in Africa.
There are about 36 species in the subfamily Petauristinae, arranged in around 13 genera. The largest is the Woolly Flying Squirrel, Eupetaurus cinereus, found in Kashmir. The two species of the genus Glaucomys are native to North America, and it is these that are most often meant when the name "flying squirrel" are used in English. They are:
- Glaucomys sylvanus, the Northern Flying Squirrel, whose range extends from Alaska to Virginia (several geographical subspecies are recognised, some of which are endangered);
- G. volans, the Southern Flying Squirrel, whose range extends from the south-eastern United States to parts of Mexico.