The four Horn Concertos by Wolfgang Amadeus Mozart are a major part of professional horn players' repertoire. The concertos were written for his friend Joseph Leutgeb (also spelled as "Leitgeb"), whom he had known since childhood. Leutgeb was clearly a skilled player, as the works are very difficult to perform on the natural horn of the period, requiring lip trills, much hand-stopping, and rapid tonguing.
Musicologists[who?] believe that Mozart conceived other horn concertos in addition to the four outlined above, based on manuscripts including an incomplete first movement from a concerto in E-flat major (K. 370b) (with which the Rondo, K. 371 was probably paired), and a fragment of the first movement of a concerto in E major (K. 494a).
Given the duration of the concerti (no more than 20 minutes each) it is quite common to find these Horn Concertos on the same CD, or in boxed sets of Mozart's concerti for wind instruments or even all his concerti. The Naxos Records CD "Complete Works for Horn & Orchestra" includes, besides the concerti, three rondos for horn and orchestra completed by musicologists. When a CD has only one of the horn concerti, it is typically paired with another concerto for a wind instrument also by Mozart.