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The skull is a bony structure in the head of most vertebrates (in particular, craniates) that supports the structures of the face and forms a protective cavity for the brain. The skull is composed of two parts: the cranium and the mandible. The skull forms the anterior most portion of the skeleton and is a product of encephalization, housing the brain, many sensory structures (eyes, ears, nasal cavity), and the feeding system.

Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, and fixing the position of the ears to help the brain use auditory cues to judge direction and distance of sounds. In some animals, the skull also has a defensive function (e.g. horned ungulates); the frontal bone is where horns are mounted.

The English word "skull" is probably derived from Old Norse "skalli" meaning bald, while the Latin word cranium comes from the Greek root κρανίον (kranion).

Human skull

In humans, as in other mammals, the aforementioned division of the skull into the cranium and mandible is not usually followed. Instead, for the purposes of describing their anatomy and enumerating their bones, mammalian and human skulls are divided differently: They are deemed to consist of two categorical parts, the neurocranium and the viscerocranium. The neurocranium (or braincase) is a protective vault surrounding the brain. The viscerocranium (also splanchnocranium or facial skeleton) is formed by the bones supporting the face. Both parts have different embryological origins.

Except for the mandible, all of the bones of the skull are joined together by sutures, rigid articulations permitting very little movement.