Great Mass in C minor, KV 427 (K 417a)

The work was composed during 1782/83. In a letter to his father Leopold dated 4 January 1783, Mozart mentioned a vow he had made to write a mass when he would bring his then fiancée Constanze as his wife to Salzburg; Constanze then sang the "Et incarnatus est" at its premiere.

The first performance took place in Salzburg on 26 October 1783. Mozart had moved to Vienna in 1781, but was paying a visit to his home town in the company of Constanze, who had not yet met his father or his sister (Nannerl).

The performance consisted of the Kyrie, Gloria and Sanctus and took place in the Church of St. Peter's Abbey in the context of a Roman Catholic mass. The performers were members of the "Hofmusik", that is the musicians employed at the court of Salzburg's ruler, Prince-Archbishop Count Hieronymus von Colloredo and thus Mozart's former colleagues.[3] There was a rehearsal in the nearby Kapellhaus on 23 October 1783.