The Bwindi Impenetrable Forest is old, complex, and biologically rich. Diverse species are a feature of the park, and it became an UNESCO World Heritage Site because of its ecological importance. Among East African forests, Bwindi has some of the richest populations of trees, small mammals, birds, reptiles, butterflies, and moths. The park's diverse species are partly a result of the large variations of elevation and habitat types in the park, and may also be because the forest was a refuge for species during glaciations in the Pleistocene epoch.

The park's forests are afromontane, which is a rare vegetation type on the African continent. Located where plain and mountain forests meet, there is a continuum of low-altitude to high altitude primary forests in the park, one of the few large tracts of East African forest where this occurs. The park has more than 220 tree species, and more than 50% of Uganda's tree species, and more than 100 fern species. The brown mahogany is a threatened plant species in the park.

Bwindi Impenetrable National Park is important for the conservation of the afromontane fauna, especially species endemic to the Western Rift Valley's mountains. It is thought to have one of the richest faunal communities in East Africa, including more than 350 bird species and more than 200 butterfly species. There are an estimated 120 mammal species in the park, of which 10 are primates,[16]:744 and more than 45 are small mammals. Along with mountain gorilla, species in the park include common chimpanzee, L'Hoest's monkey, African elephant, African green broadbill, and cream-banded swallowtail, black and white colobus, red-tailed monkeys, vervets, the giant forest hog, and small antelope species. The fish species in the park's rivers and streams are not well known. There are also many carnivores, including the side-striped jackal, African golden cat, and African civet

The park is inhabited by about 600 individual mountain gorillas (Gorilla beringei beringei), known as the Bwindi population, which makes up almost half of all the mountain gorillas in the world. The rest of the worldwide mountain gorilla population is in the nearby Virunga Mountains. A 2006 census of the mountain gorilla population in the park showed that its numbers had increased modestly from an estimated 300 individuals in 1997,to 320 individuals in 2002 to 340 individuals in 2006, and 400 in 2018. Disease and habitat loss are the greatest threat to the gorillas. Poaching is also a threat.

Research on the Bwindi population lags behind that of the Virunga National Park population, but some preliminary research on the Bwindi gorilla population has been carried out by Craig Stanford. This research has shown that the Bwindi gorilla's diet is markedly higher in fruit than that of the Virunga population, and that the Bwindi gorillas, even silverbacks, are more likely to climb trees to feed on foliage, fruits, and epiphytes. In some months, the Bwindi gorilla diet is very similar to that of Bwindi chimpanzees. It was also found that Bwindi gorillas travel farther per day than Virunga gorillas, particularly on days when feeding primarily on fruit than when they are feeding on fibrous foods. Additionally, Bwindi gorillas are much more likely to build their nests in trees, nearly always in Alchornea floribunda (locally, "Echizogwa"), a small understory tree.

Mountain gorillas are an endangered species, with an estimated total population of about 650 individuals. There are no mountain gorillas in captivity. In the 1960s and 1970s, mountain gorillas were captured to begin a population of them in captive facilities. No baby gorillas survived in captivity, and no mountain gorillas are known of that are currently in captivity

Tourists may visit the park any time during the year, although conditions in the park are more difficult during the rainy season. The park is in a remote location, and the roads are in poor condition. Tourist accommodations include a lodge, tented camps, and rooms run by the community located near the Buhoma entrance gate.

Bwindi Community Hospital provides health care to 40,000 people in the area and to visiting tourists.

Gorilla tracking is the park's main tourist attraction, and it generates much revenue for Uganda Wildlife Authority. Tourists wishing to track gorillas must first obtain a permit. Selected gorillas families have been habituated to human presence, and the number of visitors is tightly controlled to prevent risks to the gorillas and degradation of the habitat. Several tour companies are able to reserve gorilla tracking permits for prospective visitors to Bwindi. The gorillas seldom react to tourists. There are strict rules for tourists to minimize the risk of diseases passing from them to the gorillas. Uganda, Rwanda, and the Democratic Republic of the Congo are the only countries where it is possible to visit mountain gorillas. Guided walks through the forest include a walk to a waterfall, and walks for monkey watching and birding.