Mozart began to work on his monumental “Missa in c” K. 427 (417a) in the fall and winter of 1782/83. The first performance of the finished sections “Kyrie” and “Gloria” took place on Sunday, October 26th, 1783 in St. Peter in Salzburg. There was much speculation as to why Mozart did not finish his work. This edition of the great Mass in C minor is based on the Urtext edition which appeared in the New Mozart Edition and contains the “Credo” and the “Sanctus” in a reconstruction and completion by Helmut Eder.<br>