Mylodon is an extinct genus of ground sloth belonging to the family Mylodontidae, known from southern South America. With a total length of 3 to 4 m and a body mass of 1-2 tonnes, it is one of the largest mylodontids (though it was considerably exceeded in size by the mylodontid Lestodon).

The oldest finds probably date to the Lower Pleistocene; however, most of the fossil remains date to the Late Pleistocene. Its distribution ranged from southern Bolivia and the Pampas in the north southwards to the southernmost part of Patagonia at around 52-53 degrees south, the furthest south of any Pleistocene ground sloth, with some of the best known remains of the species being from the eponymous Cueva del Milodon (cave of Mylodon) in southern Chile.

In addition to skeletal remains, Mylodon is also known from preserved skin and hair. Preserved dung (coprolites) indicates that Mylodon was a primarily a grazer, feeding on grasses and sedges.

Mylodon has generally only a single recognised species, Mylodon darwini, which was described by Richard Owen in 1840 based on remains collected in the Pampas by Charles Darwin (for whom the species is named) during the Voyage of the Beagle. Some recent authors suggest that there were two species, with M. darwini restricted to the Pampas, with the Patagonian remains belonging to the separate species Mylodon listai.

Mylodon went extinct at the end of the Late Pleistocene-beginning of the Holocene, around 12–10,000 years ago, as part of the end-Pleistocene extinction event, along with other ground sloths and most large animals across the Americas. Mylodon chronologically overlapped with Paleoindians, the first humans to inhabit the Americas, evidence from several sites suggest that they may have hunted Mylodon. The extinction of Mylodon may be the result of climatic change, hunting by Paleoindians, or a combination of both factors.

Mylodon was named by Richard Owen on the basis of a nearly complete lower jaw with teeth, which was found by Charles Darwin in a consolidated gravel cliff at Bahía Blanca, during the survey expedition of HMS Beagle. At several sites, preserved hide and dung have been discovered, and are in such a state of conservation that the people who first discovered them believed they belonged to a living animal, instead of to an extinct species. The discovery of fresh-looking samples of skin and dung sparked a small wave of expeditions during the early 20th century to search for a living example of the animal. The samples have since been found to be around 10,000 years old, although they look fresh because of the extreme cold and stable conditions in the caves in which they were found.

Well preserved samples of Mylodon remains have been discovered in the Cueva del Milodón site in Patagonia, Chile along the southern flank of Cerro Benítez in the year 1896. Associated with bones of other early Patagonian animals, these remains of Mylodon date from an era earlier than 10,000 BC. The American Museum of Natural History has exhibited a sample of Mylodon dung from Argentina with a note that reads "deposited by Theodore Roosevelt".

Mylodon was a large representative of the Mylodontidae. Its total length was estimated to be around 3 to 4 m. Based on the size of the skull, a weight between 1 and 2 tonnes is assumed, with an approximate estimate of 1.65 tonnes. Thus, Mylodon had about the size of related forms such as Glossotherium or Paramylodon, but was significantly smaller than the giant Lestodon. In terms of physique, it largely corresponded with the other large ground-living sloths.