Un ballo in maschera (A Masked Ball) is an opera in three acts by Giuseppe Verdi with text by Antonio Somma. However, Somma's libretto was itself based on the five act libretto which playwright Eugène Scribe had written for Daniel Auber's 1833 opera, Gustave III, ou Le bal masqué.

Although it was to take over two years between the time of the commission and its premiere performance, that took place at the Teatro Apollo in Rome on 17 February 1859.

Scribe wrote about the assassination in 1792 of King Gustav III of Sweden who was killed as the result of a political conspiracy against him. He was shot while attending a masked ball and died 13 days later of his wounds.

In order to become the Un ballo in maschera which we know today, Verdi's opera (and his libretto) was forced to undergo a significant series of transformations, caused by a combination of censorship regulations in both Naples and Rome, as well as by the political situation in France in January 1858.