Discussing his G major Piano Concerto early in the last century, Maurice Ravel writes that it ‘is a concerto in the strictest sense of the term’. At approximately the same time, the critic F. Bonavia explains that Beethoven's Violin Concerto represents ‘no conscious departure from the accepted criterion of what a concerto should be’. But what is the ‘strictest sense’ of concerto and the ‘accepted criterion’ of its ontological status? At one level, the concerto is all-too-easy to define, at another level, intractably difficult to pin down. In broadest terms a concerto from the eighteenth century through to the present day is expected to feature a soloist or soloists interacting with an orchestra, providing a vehicle for the solo performer(s) to demonstrate their technical and musical proficiency; in practical terms, concertos demonstrate multifarious types of solo–orchestra interaction and virtuosity, often provide as much of a showcase for the orchestra as for the soloist(s) and sometimes dispense altogether with the hard-and-fast distinction between soloist(s) and orchestra. Given the extraordinary diversity of works labelled concertos, it is no wonder that critics, composers and musicologists – indeed, musicians of all shapes and sizes – have on the whole steered clear of systematic theorizing about the genre. The concerto's capacity for reinvention over its venerable 400-year history – even in 1835 a reviewer for the Gazette musicale praised Chopin's E minor Piano Concerto for ‘rejuvenating such an old form’ – has ensured its fundamental elusiveness, its longevity as a genre and, in all likelihood, its deeply ingrained popularity with the musical public at large.