In April 1782, the Austrian Emperor founded his own wind band or Harmoniemusik—a type of ensemble popular throughout the Austrian empire, particularly in Bohemia, but not hitherto especially cultivated in Vienna. Having recently settled in the capital, and already having considerable experience at composing such pieces (wind ensembles played an important part in the musical life of Salzburg), Mozart took special note of the new imperial ensemble. In September or October 1781, Mozart set to work on a new piece, ostensibly (as he told his father Leopold in a letter) for the sister-in-law of the court painter Joseph Heckel. It was scored for the usual sextet of instruments, two each of a treble instrument (in this instance clarinets), horns, and bassoons. By mid-October, the Serenade in E flat was completed, and on the 15th given its first performance at Heckel's home. On October 31, it was played again—as a nocturnal serenade to the composer himself on the occasion of his name-day.

The letter mentioned above (dated November 3) goes on to reveal Mozart's true reason for composing the serenade: "the chief reason why I composed it was in order to let Herr von Strack, who goes there [Heckel's house] every day, hear something of mine." Johann Kilian Strack was none other than valet and musical confidant to the Emperor, for which reason Mozart apparently expended much effort in cultivating him during the following year. It was all to no avail, for the influential Strack would prove no friend of Mozart.

Perhaps in order to distinguish his band from that of the many members of the aristocracy who employed wind ensembles, Joseph decided that his band should consist of not six, but eight players. In a letter written to Leopold on July 27, Mozart mentions that he has had to write a Nacht musique (a term often used for serenades) in a hurry. Formerly this was believed to be the Serenade in C minor, K. 388, which dates from much the same period, but most scholars now believe it was the revision of the E flat Serenade that Mozart was so hastily working on in order to turn it into an octet suitable for the Emperor's new ensemble. To do so, he added parts for two oboes, making revisions to the other parts where necessary; it is this octet version that is normally heard today. There are five movements; an opening Allegro maestoso is followed by a Minuetto. At the heart of the serenade lies an Adagio that fully justifies the term "night music," its warm Romantic murmuring conjures images of an enchanted nocturnal scene. A second Minuet follows before the work concludes with a final Allegro. The extraordinarily felicitous writing throughout the work speaks of a mastery of wind writing shortly to be translated with such memorable effect to the great series of piano concertos composed between 1782 and 1786.

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