A mannequin (sometimes spelled as manikin and also called a dummy, lay figure, or dress form) is a doll, often articulated, used by artists, tailors, dressmakers, window dressers and others, especially to display or fit clothing and show off different fabrics and textiles. Alternatively the term refers, or referred to, a live human fashion model.

Life-sized mannequins with simulated airways are used in the teaching of first aid, CPR, and advanced airway management skills such as tracheal intubation. During the 1950s, mannequins were used in nuclear tests to help show the effects of nuclear weapons on humans. Also referred to as mannequins are the human figures used in computer simulation to model the behavior of the human body.

Mannequin comes from the French word mannequin, which had acquired the meaning "an artist's jointed model", which in turn came from the Flemish word manneken, meaning "little man, figurine", referring to late Middle Ages practice in Flanders whereby public display of even women's clothes was performed by male pages (boys). Fashion shops in Paris ordered dolls in reed from Flemish merchants. Flanders was in terms of logistics the easiest region to import reed dolls from, as the rivers Schelde and Oise provided easy routes from Flanders to Paris. As the Flemish wrote 'manneke(n)' for 'little man' on their invoices, the Parisians pronounced this as 'mannequen', hence shifted to 'mannequin'. A mannequin is thus linguistically masculine, not feminine.

The Oxford English Dictionary gives two meanings for the term, the first being "a person employed by a dressmaker, costumier, etc., to model clothes," the second being "a model of (part of) a human figure, used for the display of clothes, etc." In the late 1800s and first part of the twentieth century, British and Australian English borrowed 'mannequin' to refer to human, invariably female, fashion models such as Loulou de la Falaise (a meaning still retained in French and other European languages) and the 1926 American Mannequin silent romantic drama film uses that sense, which has become obsolete since in American English. The meaning as a shop dummy dates from the start of World War II. Australian academic Maynard notes the ironic or symbolic potential of the interchangeability of fashion models and mannequins as humans; and of mannikins, dummies, and dolls.

Shop mannequins are derived from dress forms used by fashion houses for dress making. The use of mannequins originated in the 15th century, when miniature "milliners' mannequins" were used to demonstrate fashions for customers. Full-scale, wickerwork mannequins came into use in the mid-18th century. Wirework mannequins were manufactured in Paris from 1835.

The first female mannequins, made of papier-mâché, were made in France in the mid-19th century. Mannequins were later made of wax to produce a more lifelike appearance. In the 1920s, wax was supplanted by a more durable composite made with plaster.

Modern day mannequins are made from a variety of materials, the primary ones being fiberglass and plastic. The fiberglass mannequins are usually more expensive than the plastic ones, tend to be not as durable, but are significantly more realistic. Plastic mannequins, on the other hand, are a relatively new innovation in the mannequin field and are built to withstand the hustle of customer foot traffic usually witnessed in the store they are placed in.

Mannequins are used primarily by retail stores as in-store displays or window decoration. However, many online sellers also use them to display their products for their product photos (as opposed to using a live model).