What exactly is operetta? As a genre it seems defined by its lack of definition, by its inherent in-betweenness. On an aesthetic scale defined by opera at one end and music hall, revue and burlesque at the other, it lies somewhere in the middle. But where? True, it is difficult to disentangle operetta from the various kinds of variety theatre; it shares their fondness for a chorus line and a catchy refrain. On the other hand, the name operetta suggests a love–hate relationship with opera, its high-brow relative. ‘Little opera’ is generally shorter than opera (though what about concise classics of ‘big opera’ such as La bohème?), funnier than opera (though what about comic touchstones such as Il barbiere di Siviglia?) and less serious than opera (though the satirical bent of some operettas can be taken seriously). Perhaps, then, the difference is that it takes itself less seriously, with fewer pretensions to grandeur and more concessions to popular taste. Capitalising unashamedly on its popularity through promotional tie-ins, flaunting musical numbers poised to become well-known hits on the bandstand or on the mechanical piano, and almost invariably giving spectators the happy ending they desire: operetta is selling out, in all senses of the phrase.