Operetta (literally, "little opera") is a performance art-form similar to opera, though it generally deals with less serious topics. Often some of the libretto is spoken rather than sung (but this is true of some operas as well). Instead of moving from one musical number (literally so indicated in the scores) to another, the performers in operetta intersperse the musical segments (e. g. aria, recitative, chorus) with periods of dialogue without any singing or musical accompaniment. When music accompanies spoken dialogue for special effect, the result is technically melodrama.
Operetta is often considered less "serious" than opera, although this has more to do with the generally comic plots than with the caliber of the music.
Operetta is the precursor of the modern musical comedy. There is a fundamental but subtle distinction between the two forms. An operetta is more of a light opera with acting, whereas a musical is a play with singing. This can best be seen in the performers chosen in the two forms. An operetta's cast will normally be classically trained opera singers; indeed, there is essentially no difference between the scores for an opera and an operetta, except for the operetta's lightness. A musical uses actors who sing, but usually not in an operatic style. Having said that, W.S. Gilbert always preferred to use actors who could sing for his productions, rather than singers who could act, so it isn't an unbreakable distinction. Yet Ezio Pinza, a great Don Giovanni, scored on Broadway in South Pacific, and there are features of operetta vocal style both in Kern's Show Boat (1927) as well as in Walt Disney's animated Snow White (1937).
Operetta grew out of the French opéra comique, in which dialogue was spoken, though the opéra was not always comique: Carmen is an example of a tragic plot. Opéra comique was the form of opera in use for several centuries by most composers after the decline of tragedie lyrique. Jacques Offenbach is usually credited with having written the first operettas, such as his La Belle Hélène.
The most significant composer of operetta in the German language was the Austrian Johann Strauss, Jr. (1825-1899). His first work in this genre is Indigo und die vierzig Räuber (1871) although it was his third operetta Die Fledermaus (1874) which became the most performed operetta in the world and remained his most popular stage work. In all, he wrote 16 operettas and one opera in his lifetime. Its libretto was based on a comedy written by Offenbach's librettists. In fact, Strauss may have been convinced to write the operetta by Offenbach himself although it is now suggested that his first wife, Henrietta Treffz who repeatedly encouraged Strauss to try his hand at writing for the theater. He went on to write 16 others, mostly with great success when first premiered although now largely forgotten, since his later librettists were not very talented and he worked for some of the time independent of the plot. His operettas, waltzes, polkas, and marches often have a strongly Viennese style and his great popularity has caused many to think of him as the national composer of Austria. In fact, when his stage works were first performed during its day the Theater an der Wien never failed to draw huge crowds for his operetta premieres and many of his numbers were noisily called for encores. Franz von Suppé, a contemporary of Strauss, closely modeled his operettas after Offenbach. The Viennese tradition was carried on by Franz Lehár, Oscar Straus and Sigmund Romberg in the 20th century.
Possibly the height of English-language operetta was reached by W. S. Gilbert and Sir Arthur Sullivan, who had a long-running musical collaboration in England during the Victorian era. With Gilbert writing the dialogue and lyrics (similar to the libretto of opera) and Sullivan composing the music, the pair produced operettas which were quite popular at the time, and to some degree since. Works such as The Pirates of Penzance continue to enjoy regular performaces and even some movie adaptations. The pair of composers are popularly referred to as Gilbert and Sullivan.
See article listing of operettas.