Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths. Xenarthrans originated in South America during the late Paleocene about 60 million years ago. They evolved and diversified extensively in South America during the continent's long period of isolation in the early to mid Cenozoic Era. They spread to the Antilles by the early Miocene and, starting about 3 Mya, spread to Central and North America as part of the Great American Interchange. Nearly all of the formerly abundant megafaunal xenarthrans became extinct at the end of the Pleistocene.

Xenarthrans share several characteristics not present in other placental mammals, which suggest their ancestors were subterranean diggers for insects. The name Xenarthra derives from the two ancient Greek words ξένος (xénos), meaning "strange, unusual", and ἄρθρον (árthron), meaning "joint", and refers to their vertebral joints, which have extra articulations that are unlike other mammals. The ischium of the pelvis is also fused to the sacrum of the spine. Their limb bone structures are unusual, and they have single-color vision. The teeth of Xenarthrans are unique. Xenarthrans are also often considered to be among the most primitive of placental mammals. Females show no clear distinction between the uterus and vagina, and males have internal testicles, which are located between the bladder and the rectum. Xenarthrans have the lowest metabolic rates among therians.

Xenarthran forms and lifestyles include:

• Armadillos: Mostly small and some larger omnivores and insectivores with flexible banded body armor
• Glyptodonts: Large herbivores with a rigid semi-spherical carapace
• Pampatheres: Large herbivores (and possibly omnivores) with banded body armor
• Anteaters: Small to large specialized feeders on social insects
• Tree sloths: Medium-sized folivores specialized for life hanging upside-down in trees
• Ground sloths: Medium to very large ground-living herbivores (and possibly omnivores)
• Aquatic sloths: Thalassocnus, a medium-sized herbivore, is the only known aquatic sloth