Mozart composed numerous concertos for more than one solo instrument. He gave them various names – such as concerto for two (or three) pianos, sinfonia concertante and concertone.
Many of these works were tailored for the performance abilities of specific musicians. Two of them are among Mozart’s most famous and popular concertante works: the Concerto for flute, harp and orchestra in C major, KV 299/297c; and the Sinfonia Concertante for Violin, Viola, and Orchestra in Eb major, KV 364.
In addition to these two popular concertante works, Mozart also composed four more for multiple soloists and orchestra. Among his piano concertos, there is No. 10 for 2 pianos in E-flat major, KV 365; and the Concerto No. 7 in F for 3 Pianos and Orchestra, KV 242.
Then, there is the Concertone in C major, K.190/186 for two violins and orchestra. This name is the addition of the Italian suffix -one, meaning "big," to the word "concerto." In addition to the two principal violin soloists, the Concertone also contains frequent additions of two more solo parts, the principal cello and the first oboe, who are seated in the orchestra.
The Sinfonia concertante in E-flat major, K.297b/Anh.C 14.01– for oboe, clarinet, bassoon, horn and orchestra – is a work thought to be composed by Mozart. There is considerable dispute about the relation of the work as it is performed today to a work that Mozart composed in Paris in 1778.
Lastly, there exists an unfinished Concerto for violin, piano and orchestra: the Concerto in D for Violin, Piano and Orchestra, K.Anh.56 (315f) composed in Mannheim in 1878. All that survives today are the first 120 measures of the opening allegro. Of those 120 measures, only the first 74 are completely scored.
Mozart’s Piano Sonata in C Major KV 521 for 4-hands is a large-scale virtuoso work composed in 1787. Indeed, the work is of such exceptional brilliance, Mozart wrote to a prospective performer that he should give it to his sister right away "and tell her to tackle it at once, for it is rather difficult." Moreover, Mozart’s biographer Alfred Einstein has suggested that this sonata would gain from being played on two pianos, giving the two pianists more room to perform its wide-ranging parts. In this respect, it resembles Mozart’s equally brilliant Sonata for 2 pianos in D major, KV 448.
In KV 521, the two piano parts are of equal difficulty. Consequently, the two right-hand parts are both melodic and virtuoso in character; while the two left-hand parts usually fill out the harmony and the bass line. As many amateur pianists have discovered to their dismay, this work is far too challenging, both technically and musically, to be left to home parlour sight-reading and entertainment. It demands professional pianists of the highest calibre. But because of its 4-hand format, it doesn’t fit easily into professional piano recitals.
In order to create the orchestral accompaniment, it was necessary to fill out the harmonies and contrapuntal lines found in the two left-hand piano parts. My choice of orchestral instruments was modeled in part on the large, brilliant orchestra that Mozart employed in his unfinished Concerto for violin and piano. I utilized horns, trumpets and timpani, in addition to wood-winds and strings. However, in the woodwind section, I utilized only one flute (typical of Mozart’s concertos) and one bassoon (I figured that in most orchestras the principal bassoon would probably be the bassoon soloist.)