A comb is a device made of solid material, generally flat, always toothed, and is used in hair care for straightening and cleaning hair or other fibers. Combs are among the oldest tools found by archeologists, having been found in very refined forms already in settlements dating back to 5000 years ago in Persia.

Combs can be used for many purposes, including:

• Keeping long hair in place.
• Decorating the hair.
• Matting sections of hair for dreadlocking
• Keeping a kippa in place.
• Separating cotton fibers from seeds and other debris. The cotton gin, a mechanized version of the comb, is one of the machines that ushered the Industrial Revolution.
• Making music. Stringing a plant's leaf or a piece of paper over one side of the comb and humming with cropped lips on the opposite side dramatically increases the high-frequency harmonic content of the hum produced by the human voice box, and the resulting spread sound spectrum can be modulated by changing the resonanting frequency of the oral cavity. This was the inspiration for the kazoo. Moreover, the comb is also a lamellophone. Comb teeth have harmonic qualities of their own, determined by their shape, length, and material. A comb with teeth of unequal length, capable of producing different notes when picked, eventually evolved into the thumb piano and musical box.
• Making comb-marbled paper

Combs are also a favorite spot for police investigators to collect hair and dandruff samples that can be used in ascertaining dead or living people's identities, as well as their state of health, toxicological profiles, and so forth. The phrase often used by police detectives: "we are combing through the evidence" relates to the actual use of a large comb at the scene of a crime.

Sharing combs is a common source of parasitic infections, as one user can leave a comb with plenty of eggs or even live parasites, facilitating the transmission of lice, fleas, crabs, mites, fungi, and other undesirables.

Combs can be made out of a number of materials, most commonly wood or plastic. Ivory and tortoiseshell were once common but concerns for the animals that produce them have reduced their usage. When made from wood, Combs are largely made of boxwood, cherry wood or other fine grained wood. Good quality wooden combs are usually handmade and polished.

A hairbrush, which is larger than a comb, is also commonly used for shaping, styling and cleaning the hair.

Nit comb

Specialized combs such as "flea combs" or "nit combs" can be used to remove macroscopic parasites. A comb with teeth fine enough to remove nits is sometimes called a "fine-toothed comb", sometimes misrendered as "fine toothcomb" or merely "toothcomb", including in the metaphoric usage "go over it with a fine toothcomb" meaning a close detailed search of something.