A pillow is a support of the body at rest for comfort, therapy, or decoration. Pillows are used in different variations by many species, including humans. Some types of pillows include throw pillows, body pillows, decorative pillows, and many more. Pillows that aid sleeping are a form of bedding that supports the head and neck. Other types of pillows are designed to support the body when lying down or sitting. There are also pillows that consider human body shape for increased comfort during sleep. Decorative pillows used on beds, couches or chairs are sometimes referred to as cushions.

In contemporary western culture, pillows consist of a plain or patterned fabric envelope (known as a pillowcase) which contains a soft stuffing, typically synthetic and typically standardized in sizes and shape. Pillows have been historically made of a variety of natural materials and many cultures continue to use pillows made from natural materials in the world.

The word pillow comes from Middle English pilwe, from Old English pyle (akin to Old High German pfuliwi) and from Latin pulvinus. The first known use of the word pillow was before the 12th century.

Use of pillows evolved in animals well into prehistory, reptiles and mammals use bodies as pillows, either rest their heads on themselves, and one another, to support the head and neck. Use of pillows for comfort is evident in arboreal mammals, particularly members of Panthera and Hominoidea with several species observed selecting specific parts of tree branches for this purpose. Natural resting postures, such as the use of a laterally rotated arm or leg, may be superior to artificially created pillows in the reduction of stiffness and pain in the joints, and allows an animal to stay more alert to danger by keeping both ears open.

Pillow or cushion making is not exclusive to humans. Nest-building primates sometimes create pillow like structures. Tree dwelling orangutans typically use twigs to create them while chimpanzees have been observed making them on the ground from leaves. It has been observed in other ground dwelling mammals as well, for example Asian Elephants in captivity have been observed creating pillows from straw, though the behaviour has not been observed in the wild. Since domestication, many animals have also learned to make use of human-made pillows and cushions.

Sometime between 5 and 23 million years ago tree-dwelling great apes began building sleeping platforms, including wooden pillows, to improve their sleep. According to studies on chimpanzees that sleep up to eight to nine hours a night using specifically selected ironwood pillows, sturdy pillows enabled great apes to escape being hunted by night predators and not fall out of the trees while asleep. It is likely that this was necessitated by the evolution of large, energy-consuming brains. Though it may also have led to longer periods of REM sleep, that in turn increased their cognitive capacity.

Humans began making beds 227,000 years ago in Africa made from ash and grass. Recent evidence from 185,000 years ago at Misliya Cave shows that Neanderthals did similar. Prior to this discovery, the earliest were believed to be 77,000 years old. Much later humans began switching to use of separate stone and wood to craft pillows for increased comfort.

The earliest recorded use of the modern human device dates back to the civilizations of Mesopotamia around 7,000 BC. During this time, only the wealthy used pillows. The number of pillows symbolized status so the more pillows one owned the more affluence they held. Pillows have long been produced around the world in order to help solve the reoccurring problem of neck, back, and shoulder pain while sleeping. Besides for comfort, the pillow was also used for keeping bugs and insects out of people's hair, mouth, nose, and ears while sleeping.