The Requiem in D minor, K. 626, is a requiem mass by Wolfgang Amadeus Mozart (1756–1791). Mozart composed part of the Requiem in Vienna in late 1791, but it was unfinished at his death on 5 December the same year. A completed version dated 1792 by Franz Xaver Süssmayr was delivered to Count Franz von Walsegg, who commissioned the piece for a requiem service on 14 February 1792 to commemorate the first anniversary of the death of his wife Anna at the age of 20 on 14 February 1791.