Il signor Bruschino, ossia Il figlio per azzardo (Signor Bruschino, or The Accidental Son) is a one act operatic farce (farsa giocosa per musica) by Gioachino Rossini to a libretto by Giuseppe Maria Foppa, based upon the 1809 play Le fils par hasard, ou ruse et folie by René de Chazet and Maurice Ourry. The opera was first performed in Venice at the Teatro San Moisè on 27 January 1813.

Between 1810 and 1813, the young Rossini composed five pieces for the Teatro San Moisè, beginning with La cambiale di matrimonio (Bill of Exchange of Marriage), his first opera, and ending with Il signor Bruschino. These farse were short pieces, popular in Venice at the end of the 18th century and the beginning of the 19th century. They were intimate, with a cast of five to eight singers, always including a pair of lovers, here Sofia and Florville, at least two comic parts, here Bruschino senior, Gaudenzio and Filiberto, and one or more minor roles, here Marianna, Bruschino junior and a policeman. The style called for much visual comedy improvised by the players, and often a compulsive linguistic ‘tic’. Here, Bruschino senior often repeats the phrase "Oh, it’s so hot!". As compared with many genres of opera, acting and comedic talent is more important relative to the required singing ability. Rossini's farces also have a significant sentimental element. Overall, it has been described as "a vivacious and fast-moving musical comedy, whose graceful score reveals traces still of Cimarosa and even Mozart."

Il signor Bruschino is forward-looking in its use of new musical effects. For example, in the overture, the second violins are instructed to tap their bows on their music stands. This lighthearted, energetic overture is one of several by Rossini to have gained considerable importance in the modern concert repertoire.