Arctocyon (from Greek ''arktos'' and ''kyôn'', "bear/dog-like") is an extinct genus of large placental mammals, part of the possibly polyphyletic family Arctocyonidae.

Arctocyon was originally named as a subgenus of the bear-dog Amphicyon, though was subsequently found to belong to a genus and family of its own.

The forelimbs were powerfully muscled, the claws were curved and laterally compressed, and the digits had a strong grasping ability, suggesting that at least some species, like A. primaevus, were capable of climbing.

It was first described by Henri Marie Ducrotay de Blainville in 1841, on the basis of well-preserved fossil remains from the upper Paleocene sediments of France.

[1] In 1855, Christoph Gottfried Andreas Giebel elevated the latter name to genus level, and erected the subfamily Arctocyoninae to incorporate it, including Arctocyon, along with Agriotherium and Amphicyon.

[6] Arctocyonidae saw multiple taxonomic revisions over the coming decades, with anywhere from two[7] to four[8] subfamilies being recognised at a given time.The relationship between arctocyonids and other clades has long been uncertain.

In 2012, a phylogenetic analysis of Prolatidens waudrae, a traditional arctocyonid, recovered it as a more basal ungulate; Arctocyon, Landenodon and Thryptacodon were recovered as part of a clade sister to triisodonts and mesonychids; and the reminder of tested arctocyonids formed a polytomy basal to that clade and Diacodexis.

[12] That same year, a larger analysis by Thomas J. D. Halliday, Paul Upchurch and Anjali Goswami recovered arctocyonids as several entirely unrelated placental lineages.

By their constrained strict consensus tree, Arctocyon and Loxolophus form a clade related to pantodonts and periptychids, and the rest of Arctocyonidae is recovered close to pangolins.

[13] The type species of Arctocyon is A. primaevus, initially named by de Blainville in 1839 for remains recovered from France.

[1] Two additional species of Arctocyon, A. corrugatus and A. ferox, were named by Edward Drinker Cope in 1883, both from the Eocene of North America.

[8] The joints of the digits were highly mobile, and the flexor muscles were developed, suggesting a strong grasping ability.

[20] A. mumak had a well-developed furrow under the sustentaculum tali (a horizontal shelf on the calcaneus) and a great plantar tubercle on the navicular, suggesting a higher degree of terrestriality than in other species.

In general, it appears that Arctocyon and its close relatives, with their tusk-like canines and molariform teeth indicating an omnivorous diet, and a skeleton more like that of carnivores than that of ungulates, represented a very unusual mosaic of features, and thus their paleobiology and paleoecology are therefore very difficult to establish.