In clothing, a collar is the part of a shirt, dress, coat or blouse that fastens around or frames the neck. Among clothing construction professionals, a collar is differentiated from other necklines such as revers and lapels, by being made from a separate piece of fabric, rather than a folded or cut part of the same piece of fabric used for the main body of the garment.

A collar may be permanently attached to the main body of the garment (e.g. by stitching) or detachable.

The Oxford English Dictionary traces collar in its modern meaning to c. 1300, when collars served as neck-protecting armour.

Today's shirt collars descend from the rectangular band of linen around the neck of 16th century shirts. Separate ruffs exist alongside attached ruffled collars from the mid-16th century, usually to allow starching and other fine finishing,^{[citation needed]} or to make collar-laundering easier.

During the medieval period and sporadically thereafter, people wore ornamental collars as a form of jewelry.

Collars can be categorized as:

Collars may also be stiffened, traditionally with starch; modern wash-and-wear shirt collars may be stiffened with interfacing or may include metal or plastic collar stays. Shirt collars which are not starched are described as soft collars. The shape of collars is also controlled by the shape of the neckline to which they are attached. Most collars are fitted to a jewel neck, a neckline sitting at the base of the neck all around; if the garment opens down the front, the top edges may be folded back to form lapels and a V-shaped opening, and the cut of the collar will be adjusted accordingly.

Names for specific styles of collars vary with the vagaries of fashion. In the 1930s and 1940s, especially, historical styles were adapted by fashion designers; thus, the Victorian bertha collar — a cape-like collar fitted to a low scooping neckline — was adapted in the 1940s but generally attached to a V-neckline.