A pin-up girl or pin-up model is a model whose mass-produced pictures see wide appeal as pop culture. Pin-ups are intended for informal display. Pin-up girls are glamour models, fashion models, and actresses.

Pin-up may also refer to drawings, paintings and other illustrations done in emulation of these photos. The term was first attested to in English in 1941; however the practice is documented back at least to the 1890s.

The pin up images could be cut out of magazines or newspapers, or be from postcard or chromo-lithographs, and so on. Such photos often appear on calendars, which are meant to be pinned up anyway. Later, posters of pin-up girls were mass-produced. They became an instant hit.

Many pin ups were photographs of celebrities who were considered sex symbols. One of the most popular early pin-up girls was Betty Grable . Her poster was ubiquitous in the lockers of G.I.s during World War II. Other pin-ups were artwork, often depicting idealized versions of what some thought a particularly beautiful or attractive woman should look like. An early example of the latter type was the Gibson Girl, drawn by Charles Dana Gibson. The genre also gave rise to several well-known artists specializing in the field, including Alberto Vargas, Gil Elvgren, and George Petty, and numerous lesser artists such as Art Frahm.