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

Such gatherings were based on increasingly elaborate allegorical pageants and triumphal processions celebrating marriages and other dynastic events of late medieval court life. The famous mascarade that was long remembered as the Bal des ardents was intended as a Bal des sauvages a costumed ball to celebrate the marriage of a lady-in-waiting of Charles VI of France's queen, in Paris, January 28, 1393, where the King and five courtiers dressed as wildmen of the woods (woodwoses); a torch inadvertently set their costumes afire. Such costumed dances were a special luxury of the ducal court of Burgundy. Masquerade balls were extended into costumed public festivities in Italy during the 15th century Renaissance (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 introduced the Venetian fashion of a semi-public masquerade ball, to which one might subscribe, to London 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 Allan 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.