Great Mass in C minor (German: Große Messe in c-Moll), K. 427/417a, is the common name of the musical setting of the mass by Wolfgang Amadeus Mozart, which is considered one of his greatest works. He composed it in Vienna in 1782 and 1783, after his marriage, when he moved to Vienna from Salzburg. The large-scale work, a missa solemnis, is scored for two soprano soloists, a tenor and a bass, double chorus and large orchestra. It remained unfinished, missing large portions of the Credo and the complete Agnus Dei.
 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 to meet his family for the first time after his father's earlier opposition. Constanze then sang the "Et incarnatus est" at its premiere.
 The first performance took place in Salzburg on Sunday 26 October 1783 (the twentieth Sunday after Pentecost). 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 just the Kyrie, Gloria, Sanctus and Benedictus, as surviving parts and a score copy from ca. 1800 show. It took place in the Church of St. Peter's Abbey in the context of a Roman Catholic mass. Mozart's sister's diary mentions that the performers were the entire 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. There was a rehearsal in the nearby Kapellhaus on 23 October 1783.
 The work is incomplete, missing the Credo movements following the aria Et incarnatus est (the orchestration of the only two surviving Credo movements being incomplete) and all of the Agnus Dei. The Sanctus and the Benedictus are partially lost and require editorial reconstructions. There is a good deal of speculation concerning why the work was left unfinished. For purposes of modern performances, the editions and completions available are those by Alois Schmitt (1901, Breitkopf & Härtel), H. C. Robbins Landon (1956, Eulenburg), Helmut Eder (1985, Bärenreiter), Franz Beyer (1989, Amadeus/Edition Peters), Richard Maunder (1990, Oxford University Press/Carus Verlag), Philip Wilby (2004, Novello), Robert Levin (2005, Carus-Verlag), Clemens Kemme (2018, Breitkopf & Härtel), and Ulrich Leisinger (2019, Bärenreiter).
 The editions by Landon, Eder, Beyer, Maunder and Kemme aim to simply fill out the missing orchestrations and choral parts in the Credo and Sanctus, whereas the editions by Schmitt, Wilby and Levin aim to complete the work by either using movements from other masses or composing new music for the Credo and Agnus Dei through the use of parody or elaboration of period sketches by Mozart.
Benjamin-Gunnar Cohrs (Musikproduktion Höflich) just offers a complete Credo and an Agnus Dei. For the Credo this means a completions of the 'Credo in unum Deum' and the 'Et incarnatus est' and additional music for the rest of the Credo. This edition, therefore, is intended to be used in combination with any other version of the Mass.
Robert Xavier Rodriguez has also completed the Agnus Dei.
 Mozart later reused the music from the Kyrie and Gloria, almost without changes except for the text, in the cantata Davide penitente, K. 469. For the canatata Mozart added two new arias and a cadenza for the fugue concluding the work.
 
 The work embodies pomp and solemnity associated with the Salzburg traditions of the time, but it also anticipates the symphonic masses of Joseph Haydn in its solo-choral sharing. The mass shows the influence of Bach and Handel, whose music Mozart was studying at this time (see Gottfried van Swieten).
 On 20 August 2016 the version reconstructed by Helmut Eder was performed at the Royal Albert Hall, for the first time as part of The Proms series, by the BBC Scottish Symphony Orchestra and BBC Symphony Chorus, with Ilan Volkov conducting and featuring Louise Alder, Carolyn Sampson, Benjamin Hulett and Matthew Rose.
 Here is a selection or recordings: 
 Notes
 Sources