Arctotherium ("bear beast") is an extinct genus of short-faced bears endemic to Central and South America from the Late Pliocene to the end of the Late Pleistocene. Arctotherium migrated from North America to South America during the Great American Interchange, following the formation of the Isthmus of Panama during the late Pliocene.

The Early Pleistocene species Arctotherium angustidens is one of the largest known bears and possibly the largest terrestrial carnivorous mammal ever, with some individuals suggested to exceed one tonne in body mass and reach 3.4 to 4.3 m (11.2 to 14.1 ft) in standing height, while later species such as A. bonariense, A. tarijense and A. wingei were smaller and comparable in size to living bears. Like living bears, species of the genus were omnivorous, with the degree of meat consumption varying between species, with Arctotherium angustidens suggested to have been highly carnivorous, while A. wingei was largely herbivorous.

The last species of the genus (A. bonariense, A. tarijense and A. wingei) went extinct around 13,000-10,000 years ago as part of the end-Pleistocene extinction event, along with most other large mammals across the Americas.

Arctotherium was named by Hermann Burmeister in 1879. Arctotherium is part of the Tremarctinae subfamily of bears, otherwise known as the short faced bears, which also includes Arctodus (North American short faced bears), Plionarctos and Tremarctos (the Floridian and modern spectacled bear). In the 19th and early 20th centuries, specimens of Arctotherium were occasionally referred to Arctodus, and vice versa, along with other synonyms.

Within Arctotherium, two clades are thought to exist- A. bonariense and A. tarijense have been described as the most derived species of the genus, whilst A. vetustum and A. wingei are regarded the most archaic, even more so than A. angustidens. Of these successor species, A. tarijense and A. wingei are by far the most successful when taking into account temporal & geographic range, and the frequency of fossil finds. A separate highland form of Arctotherium is also suggested to have existed at the end of the Pleistocene, consisting of the type A. wingei specimen from Tarija and an Arctotherium sp. individual from El Rodeo, in contrast with the larger and more robust Brazilian A. wingei specimens.

Although A. wingei is only known from partial cranial and dental remains elsewhere, the A. wingei skeletons identified from Hoyo Negro in Mexico are the most complete known for its species, the Arctotherium genus and all extinct Tremarctine bears. The Hoyo Negro specimens confirm that the A. wingei had a high degree of intraspecific morphological variation.

Below is a cladogram showing proposed relationships between Arctotherium species, based on morphological data.

Size can be a useful indicator in differentiating between species of Arctotherium, but cranial and dental features need to be examined for a definite identification. The upper canine is very similar between species of Arctotherium, differing mainly in size. The canine of A. wingei is the smallest among the species. The lower canine of A. wingei presents two enamel ridges as in A. angustidens and A. tarijense, while in A. vetustum and A. bonariense there are three ridges. In A. vetustum, the distal ridge is very small and the mesial ridge is small, while in A. angustidens and A. tarijense both ridges are large.