A collar is a garment or strap that encircles the neck of a person, animal, or object.

Culture and apparel

right|thumb|150px|William Shakespeare in a sheer linen collar of the early 17th century, a direct ancestor of the modern shirt collar. main: Collar (clothing)

The Oxford English Dictionary traces collar in its modern meaning to c. 1300. Today's shirt collars descend from the ruffle created by the drawstring at the neck of the medieval chemise, through the Elizabethan ruff and its successors, the whisk collar and falling band. Separate collars exist alongside attached collars since the mid-16th century, usually to allow starching and other fine finishing.

During the Edwardian period and sporadically thereafter, ornamental collars were worn as a form of jewelry.

Restraint

thumb|right|150px|A tie-up collar used with a headcollar on a stallion. 150px|thumb|right|150px|A woman wearing a BDSM collar.

The primary function of many collars is to restrain an animal or individual.

Slave collars have been used historically, and were sometimes used prior to the abolition of slavery in the United States.

While some animal collars are strictly ornamental, most are designed to facilitate harnessing.

Bondage collars are worn by the submissive partner in BDSM.

Science and medicine

In medicine, cervical collars are used as an orthopedic device to support a patient's spinal cord and head.

Shock collars are used to administer aversion therapy.

Insect repellent collars are impregnated with chemicals that repel or kill external parasites.

Elizabethan collars prevent an animal from biting or licking at its body or scratching at its head or neck while wounds or injuries heal.

Engineering

Shaft collars are a piece of hardware used on power transmission devices as a mechanical stop, locating device, or bearing face.