Sloths are medium-sized mammals belonging to the families Megalonychidae (two-toed sloth) and Bradypodidae (three-toed sloth), classified into six species. They are part of the order Pilosa and are therefore related to anteaters, which sport a similar set of specialized claws. Extant sloths are arboreal (tree-dwelling) residents of the jungles of Central and South America, and are known for being slow-moving, and hence named "sloths". Extinct sloth species include a few species of aquatic sloths and many ground sloths, some of which attained the size of elephants.

Sloths make a good habitat for other organisms, and a single sloth may be home to moths, beetles, cockroaches, ciliates, fungi, and algae.