A masquerade ball (or masque) is an event which the participants attend in costume, usually including a mask.

Such gatherings were first held in Italy during Renaissance times (in Old Italian, maschera). They were generally elaborate dances held for members of the upper classes, and were particularly popular in Venice. They have been associated with the tradition of the Venetian Carnival.

They became popular throughout mainland Europe in the seventeenth and eighteenth centuries, sometimes with perilous results. Gustav III of Sweden was assassinated at a masquerade ball by disgruntled nobleman Jacob Johan Anckarström, an event which Eugène Scribe wrote about in his play Gustave III, and which was later made in to an opera Un Ballo in Maschera, by Giuseppe Verdi. Charles VI of France was severely burned when he performed in a masquerade ball (morisco), as one of six hairy "wild men" with costumes of flax and pitch; when they came too close to a torch, the dancers caught fire. As a result, the event became known as the Bal des Ardents or "Ball of the Fiery".

John James Heidegger, a Swiss Count, is credited with having brought the tradition into fashion in England in the early eighteenth century, with the first being held at Haymarket Opera House. Throughout the century the dances became popular, both in England and Colonial America. Its prominence did not go unchallenged; a significant anti-masquerade movement grew alongside the balls themselves. The anti-masquerade writers (among them such notables as Henry Fielding) held that the events encouraged immorality and "foreign influence". While they were sometimes able to persuade authorities to their views, enforcement of measures designed to end masquerades was at best desultory.

Masquerade balls are still held today, though in modern times the party atmosphere is emphasized and the formal dancing usually less prominent. Less formal "costume parties" may be a descendant of this tradition.

The picturesque quality of the masquerade ball has made it a favorite topic or setting in literature. Edgar Allen Poe's short story "The Masque of the Red Death" is based on the concept of a masquerade ball in which a central figure is just what he is costumed to be.