Concertos for three pianos – there are not many of them – always seem to be family affairs. Bach wrote his concerto for three harpsichords for himself and his two grown sons. The present work, likewise, was intended for a parent and two children, only this time the performers were female, and they were all amateurs: Countess Antonia Lodron and her daughters Louise and Josepha, members of the Salzburg aristocracy whom the young Mozart visited frequently.

The Countess, née d'Arco, was the sister of that Count d'Arco whom no one familiar with Mozart's biography can easily forget. A senior official at the court of Archbishop Colloredo, Count Arco had a memorable falling-out with Mozart, who wanted to leave the Archbishop's service. In the heat of the dispute, the Count immortalized himself by giving Mozart a kick in the rear, as the composer reported the incident to his father. After this confrontation, Mozart's departure from Salzburg became inevitable.

This happened in 1779. Three years earlier, the 20-year-old Mozart had no inkling of the turn events would take. Not that he was happy in provincial Salzburg; he was actively looking for employment elsewhere. Yet his situation in his hometown had not yet become untenable. He was well established in the musical life of the city, where he had many contacts, thanks in part to his father, composer and violinist Leopold Mozart, a longtime resident of Salzburg.

One area of composition Mozart had not yet cultivated extensively (despite the fact that at 20, he had been a professional composer for at least a decade) was the concerto. He had arranged concertos after other composers' works as a child, but it was only in the mid to late 1770s that he wrote his first concertos, including five for violin, one each for bassoon, flute, and oboe, as well as several for piano(s).
The Countess Lodron was a good pianist, and so were his daughters, although the younger was not very advanced in her studies. For this reason, Mozart made sure that the third piano part was not very difficult; it was later possible for him to divide the part between the first two pianos, thereby creating a version for two, rather than three, solo instruments.

The concerto opens with a march-like motif that, however, has an element of asymmetry built into it: instead of the usual construction in even-numbered measures, we have a forte idea of 3 measures followed by a piano motif of four measures. The orchestral introduction is rather short, especially if we compare it to Mozart's great Viennese concertos; nonetheless, it contains a full-fledged lyrical second theme. It is a sonata exposition in miniature. After the entrance of the soloists, the same material is repeated, considerably expanded. There is a supremely funny moment in the development section when the first two pianos engage in rather elaborate arpeggio passages while the third happily chirps along in the high register. The recapitulation is slightly varied. One of the subtle modifications is the addition of two horns in the second theme, a slight but important change. All three soloists participate in the cadenza.

The second movement is one of the most profound Adagios Mozart had written to date. It is, without any doubt, the most mature of the concerto's movements. Its expressive melody, stretched out through repeated extensions, is enriched by sensual chromatic figurations. The movement is constructed as a sonata form with a very brief development section; there is another written-out cadenza for the soloists at the end.

The finale is a rondo with a main theme cast in the form of a minuet. This movement type is quite common in the early Mozart concertos; we can also see it in the A-major violin concerto, K. 219, the Bassoon Concerto and the Piano Concerto in C (K. 246). Even the distribution of the phrases (the soloist begins, the orchestra joins in later) is standard practice.  What is special in this concerto is how the rondo form is adapted to a situation with three soloists. The first two pianos take turns as the leaders, both in the statements of the rondo theme and in the three episodes that occur between those statements. The third pianist definitely takes a “back bench” this time. There are three short cadenzas in the movement:  one for the first piano, one for the second, and one for the first and second together, but none for the third.

Mozart must have been very fond of this concerto. His letters reveal that he liked to play it whenever an opportunity presented itself. He played the second piano part at a concert in Augsburg in October 1777. The following year, when Mozart went to Paris, he included the concerto in one of his concerts there, although he did not play in it himself. And after his move to Vienna, he repeatedly asked his father to send the score along so he and his pupil Josephine Aurnhammer could perform it in the two-piano version.