Neanderthals ( nee-AN-də(r)-TAHL, nay-, -⁠THAHL; Homo neanderthalensis or sometimes H. sapiens neanderthalensis) are an extinct group of archaic humans who inhabited Europe and Western and Central Asia during the Middle to Late Pleistocene. Neanderthal extinction occurred roughly 40,000 years ago with the immigration of modern humans (Cro-Magnons), but Neanderthals in Gibraltar may have persisted for thousands of years longer.

The first recognised Neanderthal fossil, Neanderthal 1, was discovered in 1856 in the Neander Valley, Germany. At first, Neanderthal 1 was considered to be one of the lower races in accord with historical race concepts. As more fossils were discovered through the early 20th century, Neanderthals were characterised as a unique species of underdeveloped human, in particular by Marcellin Boule. By the mid-20th century, it was believed that human evolution progressed from an ape-like ancestor through a "Neanderthal phase" to modern humans. This gave way to the "Out of Africa" theory in the 1970s. With the sequencing of Neanderthal genetics first in 2010, it was discovered that Neanderthals interbred with modern humans.

Neanderthal anatomy is characterised by a long and low skull, a heavy and rounded brow ridge (supraorbital torus), an occipital bun (bony projection) at the back of the skull, strong teeth and jaws, a wide chest, and short limbs. These traits gradually became more frequent through the Middle Pleistocene of Europe, possibly due to natural selection in a cold climate, as well as genetic drift when populations collapsed during glacial periods.