The Missa brevis No. 9 in B-flat major by Wolfgang Amadeus Mozart, K. 275/272b, was probably written before September 1777 for Salzburg. The mass is scored for SATB soloists, SATB choir, violin I, violin II, 3 trombones, string bass, and organ.
The setting is divided into six movements.
- "Kyrie" Allegro, B-flat major, common time
- "Gloria" Allegro, B-flat major, 2/4
- "Credo" Allegro, B-flat major, common time
- "Sanctus" Andante, B-flat major, 3/4
- "Benedictus" Andante, E-flat major, 3/4
- "Agnus Dei" Andante, G minor, common time
In the Gloria and the Credo, Mozart eschews the traditional concluding fugues. Despite being a missa brevis, the Agnus Dei is very long and there is "a prolonged setting for soloists and choir of 'Dona nobis pacem', ending piano." The Dona nobis is set as a gavotte, "like a vaudeville and has been compared with the specimen of this genre at the end of Die Entführung."
The first known performance took place on December 21, 1777, with castrato Francesco Ceccarelli among the soloists singled out for praise for his performance, but David Schildkret has argued that it was more likely composed as early as 1772. Elsewhere church musicians were offended, such as those at Wasserburg am Inn, who found Mozart's setting "an open mockery of the holy text."