Operetta is a genre of light opera, light in terms both of music and subject matter.
Operetta grew out of the French opéra comique around the middle of the 19th century, to satisfy a need for short, light works in contrast to the full-length entertainment of the increasingly serious opéra comique. By this time, the "comique" part of the genre name had become misleading: Carmen (1875) is an example of an opéra comique with a tragic plot. The definition of "comique" meant something closer to "humanistic," meant to portray "real life" in a more realistic way, representing tragedy and comedy next to each other, as Shakespeare had done centuries earlier. With this new connotation, opéra comique had dominated the French operatic stage since the decline of tragédie lyrique.
Most researchers acknowledge that the credit for creating the operetta form should go to Hervé (1825–1892), a singer, composer, librettist, conductor, and scene painter. In 1842 he wrote the little opérette, L'Ours et le pacha, based on the popular vaudeville show by Scribe and Saintine. In 1848, Hervé made his first notable appearance on the Parisian stage, with Don Quichotte et Sancho Pança (after Cervantes), which can be considered the starting point for the new French musical theatre tradition. Hervé's most famous works are the Gounod-parody Le Petit Faust (1869) and Mam'zelle Nitouche (1883).
Jacques Offenbach further developed and popularized operetta, giving it its enormous vogue during the Second Empire and afterwards. Offenbach's earliest one-act pieces included Les deux aveugles, Le violoneux and Ba-ta-clan (all 1855), and his first full-length operetta success was Orphée aux enfers (1858). These led to the so-called "Offenbachiade": works including Geneviève de Brabant 1859, Le pont des soupirs 1861, La belle Hélène 1864, Barbe-bleue and La Vie parisienne both 1866, La Grande-Duchesse de Gérolstein 1867, La Périchole 1868 and Les brigands 1869. Offenbach's tradition was then carried on by Robert Planquette, André Messager, and others.