The Red Giant Flying Squirrel or common giant flying squirrel (Petaurista petaurista) is a species of rodent in the family Sciuridae (squirrels). It is found in a wide variety of forest–types, plantations and more open habitats with scattered trees in Southeast Asia, ranging north to the Himalayas and southern and central China. One of the largest arboreal squirrels, all populations have at least some reddish-brown above and pale underparts, but otherwise there are significant geographic variations in the colours. The taxonomic position of those in the Sundaic region is generally agreed upon, but there is considerable uncertainty about the others, which variously have been included in this or other species, or recognized as their own species.

Like other flying squirrels, the red giant flying squirrel is mostly nocturnal and able to glide (not actually fly like a bat) long distances between trees by spreading out its patagium, skin between its limbs. It is a herbivore and the female has one, infrequently two, young per litter. Although declining locally due to habitat loss and to a lesser degree hunting, it remains overall common and it is not a threatened species.

The red giant flying squirrel is among the largest flying squirrels and longest squirrels. It has a head–and–body length of 28.5–55 cm (11 in – 1 ft 9.5 in), tail length of 34–63 cm (1 ft 1.5 in – 2 ft 1 in) and weighs about 990–3,200 g (2.2–7.1 lb). Within each region, males are generally somewhat smaller, at least in weight, than females.

It varies considerably in appearance depending on subspecies and location. Roughly, it can be divided into the following subspecies groups, some of which variously have been regarded as part of this species, the Indian giant flying squirrel (P. philippensis), the red and white giant flying squirrel (P. alborufus) or the spotted giant flying squirrel (P. elegans), or their own separate species. Up until the 1980s, some authorities even listed the Indian giant flying squirrel itself as a subspecies of the red giant flying squirrel.

The red giant flying squirrel sensu stricto is the nominate subspecies group (P. p. petaurista and most other subspecies, excluding those mentioned in later groups). The distribution of this group essentially equals the Sundaic region, including Java, Sumatra, Borneo, the Thai-Malay Peninsula, nearby smaller islands, and Singapore (last Singaporean record in 1986, possibly extirpated). They generally inhabit lowlands and foothills, typically below 900–1,000 m (3,000–3,300 ft) elevation.

 Petaurista petaurista - photos from Danum Valley Sabah Malaysian Borneo.

 Petaurista petaurista melanotus - Red Giant Flying Squirrels from Koh Lanta National Park Thailand